Anatomical visualization and measurement system

ABSTRACT

A method for deploying a device in a tortuous vessel, comprising:
         placing a virtual generalized-cylinder within a virtual representation of the tortuous vessel;   measuring length along the perimeter of the virtual generalized-cylinder at a set numbers of longitudes;   determining the maximum measured length;   selecting a device based upon the maximum measured length; and   deploying the device in the tortuous vessel.

REFERENCE TO PENDING PRIOR PATENT APPLICATIONS

This patent application:

(1) is a continuation-in-part of prior U.S. patent application Ser. No.11/637,614, filed Dec. 12, 2006 now abandoned by Steven D. Pieper et al.for ANATOMICAL VISUALIZATION AND MEASUREMENT SYSTEM;

(2) is a continuation-in-part of prior U.S. patent application Ser. No.11/634,357, filed Dec. 5, 2006 now abandoned by David T. Chen et al. forANATOMICAL VISUALIZATION SYSTEM;

(3) is a continuation-in-part of prior U.S. patent application Ser. No.11/728,205, filed Mar. 23, 2007 now abandoned by Jeff Dwyer et al. forANATOMICAL VISUALIZATION AND MEASUREMENT SYSTEM;

(4) is a continuation-in-part of prior U.S. patent application Ser. No.11/145,076, filed Jun. 2, 2005 now abandoned by Jeff Dwyer et al. forANATOMICAL VISUALIZATION AND MEASUREMENT SYSTEM;

(5) is a continuation-in-part of prior U.S. patent application Ser. No.11/296,748, filed Dec. 7, 2005 now U.S. Pat. No. 7,702,137 by Jeff Dwyeret al. for ANATOMICAL VISUALIZATION AND MEASUREMENT SYSTEM; and

(6) claims benefit of prior U.S. Provisional Patent Application Ser. No.60/788,640, filed Apr. 3, 2006 by David Chen et al. for TOOLS ANDDEFINITIONS FOR MEASURING LARGE VESSELS SUCH AS THE THORACIC AORTA.

The six above-identified patent applications are hereby incorporatedherein by reference.

FIELD OF THE INVENTION

This invention relates to medical apparatus in general, and moreparticularly to anatomical visualization and measurement systems.

BACKGROUND OF THE INVENTION

Many medical procedures must be carried out at an interior anatomicalsite which is normally hidden from the view of the physician. In thesesituations, the physician typically uses some sort of scanning device toexamine the patient's anatomy at the interior site prior to, and inpreparation for, conducting the actual medical procedure. Such scanningdevices typically include CT scanners, MRI devices, X-ray machines,ultrasound devices and the like, and essentially serve to provide thephysician with some sort of visualization of the patient's interioranatomical structure prior to commencing the actual medical procedure.The physician can then use this information to plan the medicalprocedure in advance, taking into account patient-specific anatomicalstructure.

In addition to the foregoing, the physician can also use the informationobtained from such preliminary scanning to more precisely identify thelocation of selected structures (e.g., tumors and the like) which maythemselves be located within the interior of internal organs or otherinternal body structures. As a result, the physician can then moreeasily “zero in” on such selected structures during the subsequentmedical procedure.

Furthermore, in many cases, the anatomical structures of interest to thephysician may be quite small and/or difficult to identify with the nakedeye. In these situations, preliminary scanning of the patient's interioranatomical structure using high resolution scanning devices can help thephysician locate various structures of interest during the subsequentmedical procedure.

In addition to the foregoing, scanning devices of the sort describedabove are frequently also used in purely diagnostic procedures. Forexample, scanning devices of the sort described above might be used tolook for stenosis in a blood vessel, or the buildup of plaque in a bloodvessel, or a thinning of the aorta wall, etc.

In general, scanning devices of the sort described above tend togenerate two-dimensional (i.e., “2D”) images of the patient's anatomicalstructure. In many cases, the scanning devices are adapted to provide aset of 2D images, with each 2D image in the set being related to everyother 2D image in the set according to some pre-determined relationship.For example, CT scanners typically generate a series of 2D images, witheach 2D image corresponding to a specific plane or “slice” taken throughthe patient's anatomical structure. Furthermore, with many scanningdevices, the angle and spacing between adjacent image planes or slicesis very well defined, e.g., each image plane or slice may be setparallel to every other image plane or slice, and adjacent image planesor slices may be spaced a pre-determined distance apart. By way ofexample, the parallel image planes might be set 1 mm apart.

In a system of the sort just described, the physician can view each 2Dimage individually and, by viewing a series of 2D images in propersequence, can mentally generate a three-dimensional (i.e., “3D”)impression of the patient's interior anatomical structure.

Some scanning devices include, as part of their basic system, associatedcomputer hardware and software for building a 3D database of thepatient's scanned anatomical structure using a plurality of theaforementioned 2D images. For example, some CT and MRI scanners includesuch associated computer hardware and software as part of their basicsystem. Alternatively, such associated computer hardware and softwaremay be provided independently of the scanning devices, as a sort of“add-on” to the system; in this case, the data from the scanned 2Dimages is fed from the scanning device to the associated computerhardware and software in a separate step. In either case, a trainedoperator using such apparatus can create a set of scanned 2D images,assemble the data from these scanned 2D images into a 3D database of thescanned anatomical structure, and then generate various additionalimages of the scanned anatomical structure using the 3D database. Thisfeature has been found to be a very powerful tool, since it essentiallypermits a physician to view the patient's scanned anatomical structurefrom a wide variety of different viewing positions. As a result, thephysician's understanding of the patient's scanned anatomical structureis generally greatly enhanced.

In addition, scanning systems of the sort described above often includehardware and/or software tools to allow measurements to be made of thepatient's scanned anatomical structure. By way of example, many of thesesystems let a physician overlay lines on an image of the patient'sanatomical structure, and then calculate the length of these lines so asto indicate the size of the structure being viewed.

While the 2D slice images generated by the aforementioned scanningdevices, and/or the 3D database images generated by the aforementionedassociated computer hardware and software, are generally of greatbenefit to physicians, certain significant limitations still exist.

For one thing, with current systems, each scanned 2D slice image isdisplayed as a separate and distinct image, and each image generatedfrom the 3D database is displayed as a separate and distinct image.Unfortunately, physicians can sometimes have difficulty correlating whatthey see on one image with what they see on another image. By way ofexample but not limitation, physicians can sometimes have difficultycorrelating what they see on a particular scanned 2D slice image withwhat they see on a particular image generated from the 3D database.

For another thing, in many situations a physician may be viewing imagesof a patient's scanned anatomical structure in preparation forconducting a subsequent medical procedure in which a prosthetic devicemust be fitted in the patient. In these situations it can be relativelydifficult and/or time-consuming for the physician to accurately measureand record all of the anatomical dimensions needed for proper sizing ofthe prosthetic device to the patient. By way of example, in certainsituations a patient may develop an abdominal aortic aneurysm (“AAA”) inthe vicinity of the aorta's iliac branching, and repair or replacementof the affected vascular structure with a prosthetic device may beindicated. In this case it is extremely important for the physician todetermine, prior to commencing the procedure, accurate length andcross-sectional dimensions for each affected portion of blood vessel soas to ensure proper sizing of the appropriate prosthetic device to thepatient. Unfortunately, it can be difficult and/or impossible to makeaccurate anatomical measurements with existing visualization systems.This has proven to be particularly true when dealing with anatomicalstructures which extend along a tortuous path and/or which have acomplex and varied branching structure, e.g., blood vessels.

Furthermore, in many cases it may be desirable to provide a physicianwith a particular oblique view of a specified portion of a patient'sanatomical structure. For example, it may be desirable to provide aphysician with a view taken perpendicular to the length of a bloodvessel, with that view being taken at a very specific location alongthat blood vessel. Such a view might be desired for comprehensionaland/or measurement purposes. Unfortunately, it can be difficult and/orimpossible to accurately generate such a view using existingvisualization systems.

In addition to the foregoing, in many situations a physician may beinterested in accurately calculating a volume associated with a specificpart of a patient's anatomy. By way of example but not limitation, aphysician might wish to track the volume of a thrombus in an aorta overtime, or the size of a tumor during chemotherapy, etc. Unfortunately, itcan be difficult and/or impossible to accurately make such a calculationusing existing visualization systems.

Also, in many situations a physician may be interested in modeling how aparticular endoluminal prosthesis will deploy in the patient's anatomy.Unfortunately, current visualization systems do not provide simple andeffective features for providing such modeling.

OBJECTS OF THE INVENTION

Accordingly, one object of the present invention is to provide animproved anatomical visualization and measurement system for visualizingand measuring anatomical structures.

Another object of the present invention is to provide an improvedanatomical visualization and measurement system wherein a scanned 2Dslice image can be appropriately combined with an image generated from a3D database so as to create a single composite image.

Another object of the present invention is to provide an improvedanatomical visualization and measurement system wherein a marker can beplaced onto a 2D slice image displayed on a screen, and this marker willbe automatically incorporated, as appropriate, into a 3D computer modelmaintained by the system, as well as into any other 2D slice image datamaintained by the system.

Still another object of the present invention is to provide an improvedanatomical visualization and measurement system wherein a margin ofpre-determined size can be associated with a marker of the sortdescribed above, and further wherein the margin will be automaticallyincorporated into the 3D computer model, and into any other 2D sliceimage data, in association with that marker.

Yet another object of the present invention is to provide an improvedanatomical visualization and measurement system wherein the periphery ofobjects contained in a 3D computer model maintained by the system can beautomatically identified in any 2D slice image data maintained by thesystem, and further wherein the periphery of such objects can behighlighted as appropriate in 2D slice images displayed by the system.

Another object of the present invention is to provide an improvedanatomical visualization and measurement system wherein patient-specificanatomical dimensions such as length and/or cross-sectional dimensionscan be quickly, easily and accurately determined.

Still another object of the present invention is to provide an improvedanatomical visualization and measurement system which is particularlywell adapted to determine patient-specific anatomical dimensions forstructures which have a tortuous and/or branching configuration, e.g.,blood vessels.

And another object of the present invention is to provide an improvedanatomical visualization and measurement system wherein an appropriateset of scanned 2D images can be assembled into a 3D database,information regarding patient-specific anatomical structures can besegmented from the information contained in this 3D database, and thissegmented information can then be used to determine anatomical featuressuch as a centerline for the anatomical structure which has beensegmented.

Still another object of the present invention is to provide an improvedanatomical visualization and measurement system which is able to easilyand accurately present a physician with a particular oblique view of aspecified portion of a patient's anatomical structure, e.g., a viewtaken perpendicular to the length of a blood vessel, with that viewbeing taken at a very specific location along that blood vessel.

Another object of the present invention is to provide an improvedanatomical visualization and measurement system wherein patient-specificanatomical volumes can be quickly, easily and accurately determined.

And another object of the present invention is to provide an improvedanatomical visualization and measurement system wherein an appropriateset of scanned 2D images can be assembled into a 3D database,information regarding patient-specific anatomical structures can besegmented from the information contained in this 3D database, and thissegmented information can then be used to calculate desiredpatient-specific anatomical volumes.

Another object of the present invention is to provide an improved methodfor visualizing and measuring anatomical structures.

And another object of the present invention is to provide an improvedmethod wherein patient-specific anatomical dimensions such as lengthand/or cross-sectional dimensions can be quickly, easily and accuratelydetermined.

Still another object of the present invention is to provide an improvedmethod wherein an appropriate set of scanned 2D images can be assembledinto a 3D database, information regarding patient-specific anatomicalstructures can be segmented from the information contained in this 3Ddatabase, and this segmented information can then be used to determineanatomical features such as a centerline for the anatomical structurewhich has been segmented.

And another object of the present invention is to provide a method foreasily and accurately presenting a physician with a particular obliqueview of a specified portion of a patient's anatomical structure, e.g., aview taken perpendicular to the length of a blood vessel, with that viewbeing taken at a very specific location along that blood vessel.

Yet another object of the present invention is to provide an improvedmethod for quickly, easily and accurately determining patient-specificanatomical volumes.

And another object of the present invention is to provide an improvedsystem for modeling how a particular endoluminal prosthesis will deployin the patient's anatomy.

SUMMARY OF THE INVENTION

These and other objects are addressed by the present invention, whichcomprises an anatomical visualization and measurement system comprisinga first database which comprises a plurality of 2D slice imagesgenerated by scanning an anatomical structure. These 2D slice images arestored in a first data format. A second database is also provided whichcomprises a 3D computer model of the scanned anatomical structure. This3D computer model comprises a first software object which isrepresentative of the scanned anatomical structure and which is definedby a 3D geometry database.

In one embodiment of the present invention, means are provided forselecting a particular 2D slice image from the first database. Means arealso provided for inserting a second software object into the 3Dcomputer model so as to augment the 3D computer model. The secondsoftware object is also defined by a 3D geometry database, and includesa planar surface. In this embodiment of the invention, the secondsoftware object is inserted into the 3D computer model at the positionwhich corresponds to the position of the selected 2D slice imagerelative to the scanned anatomical structure. Means for texture mappingthe specific 2D slice image onto the planar surface of the secondsoftware object are also provided. Means are also provided fordisplaying an image of the augmented 3D computer model so as tosimultaneously provide a view of both the first software object and thespecific 2D slice image which has been texture mapped onto the planarsurface of the second software object.

In another embodiment of the invention, the system comprises a firstdatabase which comprises a plurality of 2D slice images generated byscanning an anatomical structure. These 2D slice images are stored in afirst data format. A second database is also provided which comprises a3D computer model of the scanned anatomical structure. This 3D computermodel comprises a first software object which is representative of thescanned anatomical structure and which is defined by a 3D geometrydatabase. In this second embodiment of the invention, means are alsoprovided for inserting a second software object into the 3D computermodel so as to augment the 3D computer model. The second software objectis also defined by a 3D geometry database, and includes a planarsurface. Furthermore, means are also provided for determining thespecific 2D slice image which corresponds to the position of the planarsurface of the second software object which has been inserted into theaugmented 3D computer model. In this embodiment of the invention, meansare also provided for texture mapping the specific 2D slice imagecorresponding to the position of that planar surface onto the planarsurface of the second software object. In this embodiment of theinvention, display means are also provided for displaying an image ofthe augmented 3D computer model to a physician so as to simultaneouslyprovide a view of the first software object and the specific 2D sliceimage which has been texture mapped onto the planar surface of thesecond software object.

In each of the foregoing embodiments of the present invention, the 3Dgeometry database may comprise a surface model.

Likewise, the system may further comprise means for inserting a markerinto the first database, whereby the marker will be automaticallyincorporated into the second database, and further wherein the markerwill be automatically displayed where appropriate in any image displayedby the system.

Also, the system may further comprise a margin of pre-determined sizeassociated with the aforementioned marker.

Additionally, the system may further comprise means for automaticallyidentifying the periphery of any objects contained in the seconddatabase and for identifying the corresponding data points in the firstdatabase, whereby the periphery of such objects can be highlighted asappropriate in any image displayed by the system.

Often, the scanned structure will comprise an interior anatomicalstructure.

In yet another form of the present invention, the visualization andmeasurement system may incorporate means for determiningpatient-specific anatomical dimensions, such as length and/orcross-sectional dimensions, using appropriate scanned 2D image data.More particularly, the visualization and measurement system may includemeans for assembling an appropriate set of scanned 2D images into a 3Ddatabase, means for segmenting information regarding patient-specificanatomical structures from the information contained in the 3D database,means for determining from this segmented information anatomicalfeatures such as a centerline for the anatomical structure which hasbeen segmented, means for specifying a measurement to be made based onthe determined anatomical feature, and means for calculating themeasurements so specified.

In a more particular form of the present invention, the visualizationand measurement system is particularly well adapted to determinepatient-specific anatomical dimensions for structures which have atortuous and/or branching configuration, e.g., blood vessels. In thisform of the invention, the visualization and measurement system isadapted to facilitate (1) assembling an appropriate set of scanned 2Dimages into a 3D database; (2) segmenting the volumetric data containedin the 3D database into a set of 3D locations corresponding to thespecific anatomical structure to be measured; (3) specifying, for eachbranching structure contained within the specific anatomical structureof interest, a branch line in the volumetric data set that uniquelyindicates that branch structure, with the branch line being specified byselecting appropriate start and end locations on two of the set ofscanned 2D images; (4) calculating, for each branching structurecontained within the specific anatomical structure of interest, acentroid path in the volumetric data set for that branching structure,with the centroid path being determined by calculating, for each scanned2D image corresponding to the branch line, the centroid for the branchstructure contained in that particular scanned 2D image; (5) applying acurve-fitting algorithm to the centroid paths determined above so as tosupply data for any portions of the anatomical structure which may liebetween the aforementioned branch lines, and for “smoothing out” anynoise that may occur in the system; and (6) applying known techniques tothe resulting space curves so as to determine the desired anatomicaldimensions.

In still another form of the present invention, the visualization andmeasurement system may incorporate means for easily and accuratelypresenting a physician with a particular oblique view of a specifiedportion of a patient's anatomical structure, e.g., a view takenperpendicular to a blood vessel, at a very specific location along thatblood vessel.

In another form of the present invention, the visualization andmeasurement system may incorporate means for more accurately measuringthe dimensions of an anatomical structure by utilizing one or moreoblique views taken along the length of that anatomical structure.

In yet another form of the present invention, the visualization andmeasurement system may incorporate means for determiningpatient-specific anatomical volumes using appropriate scanned 2D imagedata. More particularly, the visualization and measurement system mayinclude means for assembling an appropriate set of scanned 2D imagesinto a 3D database, means for segmenting information regardingpatient-specific anatomical structures from the information contained inthe 3D database, means for determining from this segmented informationanatomical volumes from the anatomical structure which has beensegmented, means for specifying a structure of interest, and means forcalculating the volume of the specified structure.

The present invention also comprises an improved method for visualizingand measuring anatomical structures.

The present invention also comprises a method for calculatingpatient-specific anatomical dimensions using appropriate scanned 2Dimage data. In one form of the present invention, the method comprisesthe steps of (1) assembling an appropriate set of scanned 2D images intoa 3D database; (2) segmenting information regarding patient-specificanatomical structures from the information contained in the 3D database,(3) determining for this segmented information anatomical features suchas a centerline for the anatomical structure which has been segmented;(4) specifying a measurement to be made based on the determinedanatomical feature; and (5) calculating the measurement so specified.

The present invention also comprises a method for easily and accuratelypresenting a physician with a particular oblique view of a specifiedportion of a patient's anatomical structure, e.g., a view takenperpendicular to a blood vessel, at a very specific location along thatblood vessel.

The present invention also comprises a method for calculatingpatient-specific anatomical volumes using appropriate scanned 2D imagedata. In one form of the present invention, the method comprises thesteps of (1) assembling an appropriate set of scanned 2D images into a3D database; (2) segmenting information regarding patient-specificanatomical structures from the information contained in the 3D database,(3) determining from this segmented information volumes for theanatomical structure which has been segmented, (4) specifying astructure of interest, and (5) calculating the volume of the specifiedstructure.

In another form of the invention, there is provided a computer-basedvisualization system for visualizing anatomical structure and a graftimplant which is to be deployed adjacent the anatomical structure,comprising:

a 3D computer model of the anatomical structure which is to bevisualized, said 3D computer model comprising at least one firstsoftware object, wherein said at least one first software objectcorresponds to the anatomical structure which is to be visualized;

a database of second software objects, wherein at least one of saidsecond software objects corresponds to a graft implant which is to bedeployed adjacent the anatomical structure;

selection apparatus for permitting a user to select said at least one ofsaid second software objects;

registration apparatus for positioning said selected at least one ofsaid second software objects into said 3D computer model so as to createan augmented 3D computer model, with said selected at least one of saidsecond software objects being positioned in said augmented 3D computermodel in proper registration with said at least one first softwareobject contained in said augmented 3D model; and

processing apparatus for generating an image of said augmented 3Dcomputer model so as to simultaneously provide a view of said at leastone first software object and said selected at least one second softwareobject.

In another form of the invention, there is provided a method forvisualizing anatomical structure and a graft implant which is to bedeployed adjacent the anatomical structure, comprising:

providing a 3D computer model of the anatomical structure which is to bevisualized, said 3D computer model comprising at least one firstsoftware object, wherein said at least one first software objectcorresponds to the anatomical structure which is to be visualized;

providing a database of second software objects, wherein at least one ofsaid second software objects corresponds to a graft implant which is tobe deployed adjacent the anatomical structure;

selecting said at least one of said second software objects;

positioning said selected at least one of said second software objectsinto said 3D computer model so as to create an augmented 3D computermodel, with said selected at least one of said second software objectsbeing positioned in said augmented 3D computer model in properregistration with said at least one first software object contained insaid augmented 3D model; and

generating an image of said augmented 3D computer model so as tosimultaneously provide a view of said at least one first software objectand said selected at least one second software object.

In another form of the invention, there is provided a visualizationsystem comprising:

a first database comprising a plurality of 2-D slice images generated byscanning an anatomical structure, said 2-D slice images being stored ina first data format; a second database comprising a 3D computer model ofsaid scanned anatomical structure, said 3D computer model comprising atleast one first software object, said at least one first software objectbeing defined by a 3-D geometry database;

insertion apparatus for selectively inserting a second software objectinto said 3D computer model so as to augment said 3D computer model,said second software object being defined by a 3D geometry database andincluding a planar surface;

determining apparatus for determining the specific 2D slice imageassociated with the position of said planar surface of said secondsoftware object when said second software object is inserted within saidaugmented 3D computer model; texture mapping apparatus for texturemapping said specific 2-D slice image onto said planar surface of saidsecond software object when said second software object is insertedwithin said augmented 3D computer model;

a third database of third software objects, wherein at least one of saidthird software objects corresponds to a graft implant which is to bedeployed adjacent the scanned anatomical structure;

selection apparatus for permitting a user to select said at least one ofsaid third software objects;

registration apparatus for selectively positioning said selected atleast one of said third software objects into said augmented 3D computermodel, with said selected at least one of said third software objectsbeing positioned in said augmented 3D computer model in properregistration with said at least one first software object contained insaid augmented 3D model; and

display apparatus for displaying an image of said augmented 3D computermodel so as to simultaneously provide a view of said (i) first softwareobject; (ii) said specific 2D slice image texture mapped onto saidplanar surface of said second software object when said second softwareobject is inserted within said augmented 3D computer model; and (iii)said at least one of said third software objects when said at least onone of said third software objects is positioned within said augmented3D computer model.

In another form of the invention, there is provided a method forvisualizing structure, comprising:

providing a first database comprising a plurality of 2-D slice imagesgenerated by scanning an anatomical structure, said 2-D slice imagesbeing stored in a first data format;

providing a second database comprising a 3D computer model of saidscanned anatomical structure, said 3D computer model comprising at leastone first software object, said at least one first software object beingdefined by a 3-D geometry database;

providing insertion apparatus for selectively inserting a secondsoftware object into said 3D computer model so as to augment said 3Dcomputer model, said second software object being defined by a 3Dgeometry database and including a planar surface;

providing determining apparatus for determining the specific 2D sliceimage associated with the position of said planar surface of said secondsoftware object when said second software object is inserted within saidaugmented 3D computer model;

providing texture mapping apparatus for texture mapping said specific2-D slice image onto said planar surface of said second software objectwhen said second software object is inserted within said augmented 3Dcomputer model;

providing a third database of third software objects, wherein at leastone of said third software objects corresponds to a graft implant whichis to be deployed adjacent the scanned anatomical structure;

selecting said at least one of said third software objects;

positioning said selected at least one of said third software objectsinto said augmented 3D computer model, with said selected at least oneof said third software objects being positioned in said augmented 3Dcomputer model in proper registration with said at least one firstsoftware object contained in said augmented 3D model; and

displaying an image of said augmented 3D computer model so as tosimultaneously provide a view of (i) said first software object; (ii)said at least one of said third software objects; and (iii) saidspecific 2D slice image texture mapped onto said planar surface of saidsecond software object when said second software object is insertedwithin said augmented 3D computer model.

In another form of the invention, there is provided a method fordeploying a device in a tortuous vessel, comprising:

placing a virtual generalized-cylinder within a virtual representationof the tortuous vessel;

measuring length along the perimeter of the virtual generalized-cylinderat a set numbers of longitudes;

determining the maximum measured length;

selecting a device based upon the maximum measured length; and

deploying the device in the tortuous vessel.

In another form of the invention, there is provided a method formeasuring a length along a tortuous vessel, comprising:

placing a virtual generalized-cylinder within a virtual representationof the tortuous vessel;

measuring length along the perimeter of the virtual generalized-cylinderat a set numbers of longitudes; and

determining at least one of the maximum measured length and the minimummeasured length.

In another form of the invention, there is provided an apparatus for usein measuring a length along a tortuous vessel, comprising:

a first component for placing a virtual generalized-cylinder within avirtual representation of the tortuous vessel;

a second component for measuring length along the perimeter of thevirtual device at a set numbers of longitudes; and

a third component for determining at least one of the maximum measuredlength and the minimum measured length.

In another form of the invention, there is provided a method forcalculating vessel volume along a medial curve, comprising:

determining a region of interest from a medical image that defines thevessel volume to be measured;

partitioning the volume of the region of interest into sub-volumes;

removing selected sub-volumes from the volume of the region of interest;and

calculating the vessel volume by combining the remaining sub-volumesafter removal of the previously selected sub-volumes.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore fully disclosed or rendered obvious by the following detaileddescription of the preferred embodiments of the invention, which is tobe considered together with the accompanying drawings wherein likenumbers refer to like parts, and further wherein:

FIG. 1 is a schematic view showing a scanning device for generating aset of 2D images of the anatomy of a patient;

FIG. 2 is a 2D slice image corresponding to an axial slice taken throughthe abdomen of an individual;

FIG. 3 shows a series of data frames corresponding to 2D slice imagesarranged in a parallel array;

FIG. 4 is a schematic view showing the scanning data contained within anexemplary data frame;

FIG. 5 shows scanning data stored in a first storage device or mediumbeing retrieved, processed and then stored again in a second datastorage device or medium;

FIG. 6 is a schematic view of a system for retrieving and viewingscanning data;

FIG. 7 is a schematic view of a unit cube for use in defining polygonalsurface models;

FIG. 8 illustrates the data file format of the polygonal surface modelfor the simple unit cube shown in FIG. 7;

FIGS. 9A-9F illustrate a variety of menu choices which may be utilizedin connection with the present invention;

FIG. 10 illustrates an image drawn to a window using the data containedin the 3D computer model associated with the present invention;

FIG. 11 illustrates a 2D slice image drawn to a window in accordancewith the present invention;

FIG. 12 illustrates a composite image formed from information containedin both the 3D computer model and the 2D slice image data structure;

FIG. 13 is a schematic illustration showing the relationship betweenaxial slices, sagittal slices and coronal slices;

FIG. 14 illustrates three different images being displayed on a computerscreen at the same time, with a marker being incorporated into each ofthe images;

FIG. 15 illustrates a marker shown in an image generated from the 3Dcomputer model, with the marker being surrounded by a margin ofpre-determined size;

FIG. 16 illustrates a 2D slice image, wherein the periphery of an objecthas been automatically highlighted by the system;

FIG. 17 is a schematic illustration showing various anatomicalstructures on a 2D slice image, where that 2D slice image has been takenaxially through the abdomen of a patient, at a location above theaortic/iliac branching;

FIG. 18 is a schematic illustration showing various anatomicalstructures on another 2D slice image, where that 2D slice image has beentaken through the abdomen of the same patient, at a location below theaortic/iliac branching;

FIGS. 17A and 18A are schematic illustrations like those of FIGS. 17 and18, respectively, except that segmentation has been performed in the 3Ddatabase so as to highlight the patient's vascular structure;

FIG. 19 is a schematic illustration showing that same patient's vascularstructure in the region about the aortic/iliac branching, with branchlines having been specified for the patient's aorta and two iliacbranches;

FIG. 20 is a schematic illustration showing how the centroid iscalculated for the branch structure contained in a particular scanned 2Dimage;

FIG. 21 is a schematic illustration showing the tortuous centroid pathcalculated for each of the respective branch lines shown in FIG. 19;

FIG. 22 is a schematic illustration showing the space curve determinedby applying a curve-fitting algorithm to two of the centroid paths shownin FIG. 21, whereby the structure between the branch lines is filled outand the centroid data “smoothed” through a “best fit” interpolationtechnique;

FIG. 23 is a flow chart illustrating how patient-specific anatomicaldimensions can be determined from scanned 2D image data in accordancewith the present invention;

FIG. 24 is a schematic view showing an oblique slice polygon disposedperpendicular to the centerline of a blood vessel;

FIG. 25 is a cumulative sum table for calculating lengths along ananatomical structure;

FIG. 26 illustrates a centerline length calculation dialogue box drawnto a window in a display;

FIG. 27 illustrates a 3D graphical icon which has been inserted into the3D model and which is visible on the display so as to show the portionof the centerline which has been specified by the physician for a lengthcalculation;

FIG. 28 is a cumulative sum table for calculating volumes with respectto an anatomical structure;

FIG. 29 illustrates a volume calculation dialogue box drawn to a windowin a display;

FIG. 30 illustrates a 3D graphical icon which has been inserted into the3D model and which is visible on the display so as to show the volumewhich has been specified by the physician using the volume calculationdialogue box;

FIG. 31 is a schematic representation of a software object representingthe aorta of a patient;

FIG. 32 is a schematic representation of the software object of FIG. 31in which the aorta has been rendered transparent;

FIG. 33 is a schematic representation of a virtual graft deployed in theaorta of FIG. 31;

FIG. 34 is a schematic representation of a virtual graft deployed in theaorta;

FIG. 35 is a schematic representation of a Manufacturer Specific VirtualGraft (MSVG) before docking of contralateral limb;

FIG. 36 is a schematic representation of a Manufacturer Specific VirtualGraft (MSVG) after docking of contralateral limb;

FIG. 37 is a schematic representation of a Manufacturer Specific VirtualGraft (MSVG), with the yellow zone representing “oversizing”;

FIG. 38 is a schematic representation of a Manufacturer Specific VirtualGraft (MSVG) Designer;

FIG. 39 is a schematic representation of a Manufacturer Specific VirtualGraft (MSVG) Product Listing;

FIG. 40 is a schematic representation of an Order Form PDF;

FIG. 41 is a schematic representation of “Twist Lines”;

FIG. 42 is a schematic representation of a resultant MSVG;

FIG. 43 is a schematic representation of an MSVG spline creation;

FIG. 44 is a schematic representation of an MSVG contact model;

FIG. 45 illustrates a screen display from one preferred construction ofthe present invention, wherein the display simultaneously provides a 2Dslice window and a 3D model window, and further wherein the imagesillustrate Native Iliac Rotation departing from the coronal plane;

FIG. 46 is a schematic representation of the centerlines for the leftiliac (LIL) branch, the right iliac (RIL) branch and the aorta (AO);

FIG. 47 is a schematic representation showing the calculation of NativeIliac Rotation off the coronal plane;

FIG. 48 is a schematic representation comparing the Twisteroo™ and theTwisterooNIR™ products for a patient having a 53 degree Native IliacRotation;

FIG. 49 is another schematic representation comparing the Twisteroo™ andthe TwisterooNIR™ products for a patient having a 53 degree Native IliacRotation;

FIG. 50 is a schematic representation of a sheath-sizing tool;

FIG. 51 is a schematic representation of left and right iliac diameterplots;

FIGS. 52 and 53 are schematic representations showing a tortuosity plotbased on the ratio of curved to straight-line lengths;

FIG. 54 is a schematic representation showing the geometry of a bloodvessel, and two planes in space;

FIG. 55 is a schematic representation showing the geometry of the bloodvessel and two planes in space, and points along a centerline of ananatomical object;

FIG. 56 is a schematic representation showing the geometry of the bloodvessel and two planes in space, points along a centerline of ananatomical object and an angle calculation;

FIG. 57 shows the distances in millimeters between inner curves, centercurves, and outer curves;

FIG. 58 is a schematic representation of a virtual thoracic graftvirtually emplaced in situ;

FIG. 59 is a schematic representation of the anatomical region ofinterest showing blood flow (in red), calcified plaque (in yellow), andthrombus (in white);

FIG. 60 is a schematic representation showing a volume region defined bytwo oblique MPR planes;

FIG. 61 is a schematic representation showing the surface model of atarget volume;

FIG. 62 is a schematic representation showing the original surfacemodels of TAA data before the oblique volume removal;

FIG. 63 is a schematic representation showing the surface models for thestart and end oblique planes at slices 65 and 360, respectively;

FIG. 64 is a schematic representation showing the difficult case wherethe start and end oblique planes are at slices 115 and 360,respectively;

FIG. 65 is a schematic representation showing the volume oblique removalmethod leading to an incorrect result due to use of a single flood;

FIG. 66 is a schematic representation showing anterior-posterior (AP)view of the surface model with cut plane after volume oblique removal;

FIG. 67 is a schematic representation showing detail of the transitionregion from ascending to descending arch of TAA; and

FIG. 68 shows a graphical user interface (GUI) for use with the volumeoblique measurement apparatus.

Listing 1 is a pseudo code of an algorithm used to calculate lengthalong the longitude of a virtual generalized cylinder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Basic System

Looking first at FIG. 1, a scanning device 5 is shown as it scans theinterior anatomical structure of a patient 10, as that patient 10 lieson a scanning platform 15.

Scanning device 5 is of the sort adapted to generate scanning datacorresponding to a series of 2D images, where each 2D image correspondsto a specific viewing plane or “slice” taken through the patient's body.Furthermore, scanning device 5 is adapted so that the angle and spacingbetween adjacent image planes or slices can be very well defined, e.g.,each image plane or slice may be set parallel to every other image planeor slice, and adjacent image planes or slices may be spaced apre-determined distance apart. By way of example, the parallel imageplanes might be set 1 mm apart.

The scanning data obtained by scanning device 5 can be displayed as a 2Dslice image on a display 20, and/or it can be stored in its 2D sliceimage data form in a first section 23 of a data storage device or medium25. Furthermore, additional information associated with the scanningdata (e.g., patient name, age, etc.) can be stored in a second section27 of data storage device or medium 25.

By way of example, scanning device 5 might comprise a CT scanner of thesort manufactured by GE Medical Systems of Milwaukee, Wis.

By way of further example, a 2D slice image of the sort generated byscanning device 5 and displayed on display 20 might comprise the 2Dslice image shown in FIG. 2. In the particular example shown in FIG. 2,the 2D slice image shown corresponds to an axial slice taken through anindividual's abdomen and showing, among other things, that individual'sliver.

Scanning device 5 may format its scanning data in any one of a number ofdifferent data structures. By way of example, scanning device 5 mightformat its scanning data in the particular data format used by a CTscanner of the sort manufactured by GE Medical Systems of Milwaukee,Wis. More specifically, with such a scanning device, the scanning datais generally held as a series of data “frames”, where each data framecorresponds to a particular 2D slice image taken through the patient'sbody. Furthermore, within each data frame, the scanning data isgenerally organized so as to represent the scanned anatomical structureat a particular location within that 2D slice image. Such a datastructure is fairly common for scanning devices of the sort associatedwith the present invention. However, it should be appreciated that thepresent invention is not dependent on the particular data formatutilized by scanning device 5. For the purposes of the presentinvention, the scanning data provided by scanning device 5 can beformatted in almost any desired data structure, so long as that datastructure is well defined, whereby the scanning data can be retrievedand utilized as will hereinafter be disclosed in further detail.

For purposes of illustrating the present invention, it can be convenientto think of the scanning data generated by scanning device 5 as beingorganized in the data structures schematically illustrated in FIGS. 3and 4.

More particularly, in FIG. 3, a series of data frames 30A, 30B, 30C,etc. are shown arranged in a parallel array. Each of these data frames30A, 30B, 30C, etc. corresponds to a particular 2D slice image takenthrough the patient's body by scanning device 5, where the 2D sliceimages are taken parallel to one another. In addition, adjacent imageplanes or slices are spaced apart by a constant, pre-determineddistance, e.g., 1 mm. It will be appreciated that data frames 30A, 30B,30C, etc. collectively form a volumetric data set which isrepresentative of the patient's scanned anatomical structure.

Furthermore, in FIG. 4, the scanning data contained within an exemplarydata frame 30A is shown represented in an X-Y coordinate scheme so as toquickly and easily identify the scanned anatomical structure disposed ata particular location within that 2D slice image. Typically, thescanning data relating to a particular X-Y coordinate represents animage intensity value. This image intensity value generally reflectssome attribute of the specific anatomical structure being scanned, e.g.,the tissue density.

As noted above, the scanning data generated by scanning device 5 isstored in its 2D slice image data form in first section 23 of datastorage device or medium 25, with the scanning data being stored in aparticular data format as determined by the manufacturer of scanningdevice 5.

In accordance with the present invention, and looking now at FIG. 5, thescanning data stored in first section 23 of data storage device ormedium 25 is retrieved, processed and then stored again in a datastorage device or medium 30.

More particularly, the scanning data stored in first section 23 of datastorage device or medium 25 is retrieved and processed so as to convertthe scanning data generated by scanning device 5 from its 2D slice imagedata form into a 3D computer model of the patient's anatomicalstructure. This 3D computer model is then stored in a first section 35of data storage device or medium 30.

In addition, the scanning data stored in first section 23 of datastorage device or medium 25 is retrieved and processed as necessary soas to convert the scanning data into a preferred data format for the 2Dslice image data. The 2D slice image data is then stored in thispreferred data format in second section 40 of data storage device ormedium 30.

Furthermore, the additional information associated with the scanningdata (e.g., patient name, age, etc.) which was previously stored insecond section 27 of data storage device or medium 25 can be stored in athird section 42 of data storage device or medium 30.

In accordance with the present invention, once the 3D computer model hasbeen stored in first section 35 of data storage device or medium 30, andthe 2D slice image data has been stored in a preferred data format insecond section 40 of data storage device or medium 30, a physician canthen use an appropriately programmed computer to access the 3D computermodel stored in first section 35 of data storage device or medium 30,and/or the 2D slice image data stored in second section 40 of datastorage device or medium 30, to generate desired patient-specificimages.

More particularly, and looking now at FIG. 6, once the 3D computer modelhas been stored in first section 35 of data storage device or medium 30,and the 2D slice image data has been stored in a preferred data formatin second section 40 of data storage device or medium 30, a physiciancan use an appropriately programmed computer 50, operated by inputdevices 55, to access the 3D computer model stored in first section 35of data storage device or medium 30, and/or the 2D slice image datastored in second section 40 of data storage device or medium 30, so asto generate the desired patient-specific images and display those imageson a display 60.

To this end, it will be appreciated that the specific data structureused to store the 3D computer model in first section 35 of data storagedevice or medium 30, and the specific data structure used to store the2D slice image data in second section 40 of data storage device ormedium 30, will depend on the specific nature of computer 50 and on theparticular operating system and application software being run oncomputer 50.

In general, however, the 3D computer model contained in first section 35of data storage device or medium 30 is preferably structured as acollection of software objects, with each software object being definedby a polygonal surface model of the sort well known in the art. By wayof example, a scanned anatomical structure such as a human liver mightbe modeled as three distinct software objects, with the outer surface ofthe general mass of the liver being one software object, the outersurface of the vascular structure of the liver being a second softwareobject, and the outer surface of a tumor located in the liver being athird software object. By way of further example, FIGS. 7 and 8illustrate a typical manner of defining a software object by a polygonalsurface model. In particular, FIG. 7 illustrates the vertices of a unitcube set in an X-Y-Z coordinate system, and FIG. 8 illustrates the datafile format of the polygonal surface model for this simple unit cube. Asis well known in the art, more complex shapes such as human anatomicalstructure can be expressed in corresponding terms.

Furthermore, the 3D computer model contained in first section 35 of datastorage device or medium 30 is created by analyzing the 2D slice imagedata stored in first section 23 of data storage device or medium 25using techniques well known in the art. For example, the 2D slice imagedata stored in first section 23 of data storage device or medium 25might be processed using the well known “Marching Cubes” algorithm,which is a so-called “brute force” surface construction algorithm thatextracts isodensity surfaces from a volumetric data set, producing fromone to five triangles within voxels that contain the surface.Alternatively, the 2D slice image data stored in first section 23 ofdata storage device or medium 25 might be processed into the 3D computermodel stored in first section 35 of data storage device or medium 30 bysome other appropriate modeling algorithm so as to yield the desired 3Dcomputer model which is stored in first section 35 of data storagedevice or medium 30.

As noted above, the specific data structure used to store the 2D sliceimage data in second section 40 of data storage device or medium 30 willalso depend on the specific nature of computer 50 and on the particularoperating system and application software being run on computer 50.

In general, however, the 2D slice image data contained in second section40 of data storage device or medium 30 is preferably structured as aseries of data “frames”, where each data frame corresponds to aparticular 2D slice image taken through the patient's body, and wherethe scanning data within each data frame is organized so as to representthe scanned anatomical structure at a particular location within that 2Dslice image.

In the present invention, it is preferred that computer 50 comprise aPower PC-based, Macintosh operating system (“Mac OS”) type of computer,e.g. a Power PC Macintosh 8100/80 of the sort manufactured by AppleComputer, Inc. of Cupertino, Calif. In addition, it is preferred thatcomputer 50 be running Macintosh operating system software, e.g. Mac OSVer. 7.5.1, such that computer 50 can readily access a 3D computer modelformatted in Apple's well-known QuickDraw 3D data format and displayimages generated from that 3D computer model, and such that computer 50can readily access and display 2D images formatted in Apple's well-knownQuickTime image data format. Input devices 55 preferably comprise theusual computer input devices associated with a Power PC-based, Macintoshoperating system computer, e.g., input devices 55 preferably comprise akeyboard, a mouse, etc.

In view of the foregoing, in the present invention it is also preferredthat the 3D computer model contained in first section 35 of data storagedevice or medium 30 be formatted in Apple's QuickDraw 3D data format,whereby the Mac OS computer 50 can quickly and easily access the 3Dcomputer model contained in first section 35 of data storage device ormedium 30 and display images generated from that 3D computer model ondisplay 60.

In view of the foregoing, in the present invention it is also preferredthat the 2D slice image data contained in second section 40 of datastorage device or medium 30 be formatted in Apple's QuickTime image dataformat. In this way computer 50 can quickly and easily display thescanned 2D slice images obtained by scanning device 5. It will beappreciated that, to the extent that scanning device 5 happens to formatits scanning data in the preferred QuickTime image data format, noreformatting of the 2D slice image data will be necessary prior tostoring the 2D slice image data in second section 40 of data storagedevice or medium 30. However, to the extent that scanning device 5happens to format its scanning data in a different data structure,reformatting of the 2D slice image data will be necessary so as to putit into the preferred QuickTime image data format. Such image datareformatting is of the sort well known in the art.

As a result of the foregoing, it will be seen that a physician operatingcomputer 50 through input devices 55 can generate a desired image fromthe 3D computer model contained within first section 35 of data storagedevice or medium 30. In particular, the physician can use input devices55 to (1) open a window on display 60, (2) instruct the computer as tothe desired angle of view, (3) generate the corresponding image of thescanned anatomical structure from the desired angle of view, using the3D computer model contained within first section 35 of data storagedevice or medium 30, and (4) display that image in the open window ondisplay 60.

In addition, a physician operating computer 50 through input devices 55can display a desired 2D slice image from the 2D slice image datacontained within second section 40 of data storage device or medium 30.In particular, the physician can use input devices 55 to (1) open awindow on display 60, (2) select a particular 2D slice image containedwithin second section 40 of data storage device or medium 30, and (3)display that slice image in the open window on display 60.

More particularly, and looking now at FIGS. 9A-9F, computer 50 ispreferably programmed so as to provide a variety of pre-determined menuchoices which may be selected by the physician operating computer 50 viainput devices 55.

Thus, for example, if the physician wishes to produce a desired imagefrom the 3D computer model contained within first section 35 of datastorage device or medium 30, the physician uses input devices 55 toinvoke the command to display the 3D computer model; the software thencreates a window to display the image, it renders an image from the 3Dcomputer model contained within first section 35 of data storage deviceor medium 30, and then displays that image in the open window on display60. By way of example, FIG. 10 illustrates an image drawn to a windowusing the data contained in the 3D computer model stored in firstsection 35 of data storage device or medium 30. The physician can useinput devices 55 to instruct the image rendering software as to thespecific angle of view desired. In particular, computer 50 is preferablyprogrammed so that the physician can depress a mouse key and then dragon the object so as to rotate the object into the desired angle of view.Additionally, computer 50 is preferably programmed so that the physiciancan also use the keyboard and mouse to move the view closer in orfurther out, or to translate the object side to side or up and downrelative to the image plane. Programming to effect such computeroperation is of the sort well known in the art.

In a similar manner, the physician can use menu choices such as thoseshown in FIGS. 9A-9F to open a window on the display 60 and then todisplay in that window a desired 2D slice image from second section 40of data storage device or medium 30. Computer 50 is programmed so thatthe physician can select between different slice images by means ofinput devices 55. By way of example, FIG. 11 illustrates a 2D sliceimage drawn to a window by the operating system using the data containedin second section 40 of data storage device or medium 30. In this case,computer 50 is programmed so that, by dragging icon 70 back and forthalong slider 75, the physician can “leaf” back and forth through thecollection of axial slices, i.e., in the example of FIG. 11, in whichaxial slice #21 is displayed, dragging icon 70 to the left might causeaxial slice #20 to be displayed, and dragging icon 70 to the right mightcause axial slice #22 to be displayed. Additionally, computer 50 ispreferably programmed so that the physician can also step the image fromthe current slice number to a previous or following slice number byusing menu commands or by clicking the mouse cursor on the single stepicons 76 set at the right side of slider 75. Computer 50 is preferablyalso programmed so that menu commands are provided to change the slicewindow display directly to the first or last slice image in the 2D sliceimage set, or to change the slice window display to a user-specifiedslice number. Programming to effect such computer operation is of thesort well known in the art.

As a consequence of using the aforementioned hardware and softwarearchitecture (i.e., the Macintosh computer, the Mac OS, the AppleQuickDraw 3D data format and software, and the Apple QuickTime imagedata format and software, or some equivalent hardware and software), itis possible to insert an additional software object into the 3D computermodel contained within first section 35 of data storage device or medium30. In particular, it is possible to insert an additional softwareobject having a “blank” planar surface into the 3D computer model.Furthermore, using the computer's image rendering software, it ispossible to texture map a 2D slice image from second section 40 of datastorage device or medium 30 onto the blank planar surface of theinserted software object. Most significantly, since the 3D computermodel is created out of the same scanning data as the 2D slice images,it is possible to determine the specific 2D slice image whichcorresponds to a given position of the blank planar surface within the3D computer model. Accordingly, with the present invention, when animage is generated from the 3D computer model, both 3D model structureand 2D slice image structure can be simultaneously displayed in properregistration with one another, thereby providing a single compositeimage of the two separate images. See, for example, FIG. 12, which showssuch a composite image. Again, computer 50 is programmed so that thephysician can use input devices 55 to instruct the operating system'simage rendering software as to where the aforementioned “additional”software object is to be inserted into the model and as to theparticular angle of view desired. Programming to effect such computeroperation is of the sort well known in the art.

Additionally, computer 50 is also programmed so that (1) the physiciancan use input devices 55 to select a particular 2D slice image from thesecond section 40 of data storage device or medium 30, and (2) thecomputer will then automatically insert the aforementioned additionalsoftware object into the 3D computer model so that the object's “blank”planar surface is located at the position which corresponds to theposition of the selected 2D slice image relative to the scannedanatomical structure. Again, programming to effect such computeroperation is of the sort well known in the art.

In the foregoing description of the present invention, the 2D sliceimage data generated by scanning device 5 has generally been discussedin the context of the standard “axial” slice images normally generatedby scanning devices of the type associated with this invention. However,it is to be appreciated that the present invention is also adapted toutilize sagittal and/or coronal 2D slice images. Furthermore, it is alsoto be appreciated that the present invention is adapted to utilizeoblique slice images of the type hereinafter described.

More particularly, and looking next at FIG. 13, the relative orientationof axial, sagittal and coronal slice images are shown in the context ofa schematic view of a human body 80. Scanning device 5 will normallygenerate axial slice image data when scanning a patient. In addition, inmany cases scanning device 5 will also assemble the axial slice datainto a 3D database (i.e., a volumetric data set) of the scannedanatomical structure, and then use this 3D database to generate acorresponding set of sagittal and/or coronal 2D slice images. In theevent that scanning device 5 does not have the capability of generatingthe aforementioned sagittal and/or coronal 2D slice images, suchsagittal and/or coronal 2D slice images may be generated from a set ofthe axial 2D images in a subsequent operation, using computer hardwareand software of the sort well known in the art. Alternatively, ifdesired, computer 50 may be programmed to render such sagittal and/orcoronal 2D slices “on the fly” from the 2D slice image data contained insecond section 40 of data storage device or medium 30.

In connection with the present invention, the sagittal and coronal 2Dslice image data may be stored with the axial slice image data in secondsection 40 of data storage device or medium 30. Preferably thesesagittal and coronal slice images are stored in exactly the same dataformat as the 2D axial slice images, whereby they may be easily accessedby computer 50 and displayed on display 60 in the same manner as hasbeen previously discussed in connection with axial 2D slice images. As aresult, axial, sagittal and coronal 2D slice images can be displayed ondisplay 60, either individually or simultaneously in separate windows,in the manner shown in FIG. 14. Furthermore, when generating a compositeimage of the sort shown in FIG. 12 (i.e., an image generated from boththe 3D computer model contained in first section 35 of data storagedevice or medium 30 and a 2D slice image contained in second section 40of data storage device or medium 30), the composite image can be createdusing axial, sagittal or coronal 2D slice images, as preferred.

It is also to be appreciated that the system of the present invention isalso configured so as to generate and utilize oblique 2D slice imagedata in place of the axial, sagittal and coronal slice image datadescribed above. More particularly, computer 50 is programmed so that aphysician can use input devices 55 to specify the location of theoblique 2D slice image desired, and then computer 50 generates that 2Dslice image from the volumetric data set present in second section 40 ofdata storage device or medium 30 (i.e., from the collection of 2D sliceimages contained in second section 40 of data storage device or medium30).

It should be appreciated that data storage device or medium 30 cancomprise conventional storage media (e.g., a hard disk, a CD ROM, a tapecartridge, etc.), which can be located either on-site or at a remotelocation linked via appropriate data transfer means.

Markers and Margins

In a further aspect of the present invention, computer 50 is programmedso that a physician can display a specific 2D slice image in a windowopened on display 60, place a marker into that specific 2D slice imageusing a mouse or other input device 55, and then have that markerautomatically incorporated into both (i) the 3D computer model containedin first section 35 of data storage device or medium 30, and (ii) anyappropriate 2D slice image data contained in second section 40 of datastorage device or medium 30. As a result, when images are thereaftergenerated from the 3D computer model contained in first section 35 ofdata storage device or medium 30, and/or from the 2D slice image datacontained in second section 40 of data storage device or medium 30,these subsequent images will automatically display the marker whereappropriate. See, for example, FIG. 14, which shows one such marker 85displayed in its appropriate location in each of the three displayed 2Dslice images, i.e., in axial slice image 90, sagittal slice image 95,and coronal slice image 100. It is to be appreciated that it is alsopossible for marker 85 to be displayed where appropriate in an imagegenerated from the 3D computer model contained in first section 35 ofdata storage device or medium 30; see, for example, FIG. 15, which showssuch a marker 85 being displayed in the image.

In yet another aspect of the present invention, computer 50 isprogrammed so that a physician can generate a “margin” of somepredetermined size around such a marker. Thus, for example, in FIG. 15,a margin 105 has been placed around marker 85. In this respect it is tobe appreciated that margin 105 will appear as a 3-dimensional sphericalshape around marker 85, just as marker 85 appears as a 3-dimensionalshape, since the view of FIG. 15 is generated from the 3D computer modelcontained in first section 35 of data storage device or medium 30.Alternatively, where marker 85 and margin 105 are displayed in thecontext of 2D slice images, the marker and margin will appear as simplecircles. Margin 105 can be used by a physician to determine certainspatial relationships in the context of the anatomical structure beingdisplayed on the computer.

Peripheral Highlighting

It is also to be appreciated that, inasmuch as the 3D computer modelcontained in first section 35 of data storage device or medium 30constitutes a plurality of software objects defined by polygonal surfacemodels, it is possible to identify the periphery of any such objects inany corresponding 2D slice image data contained in second section 40 ofdata storage device or medium 30. As a result, it is possible tohighlight the periphery of any such object in any 2D slice imagesdisplayed on display 60. Thus, in another aspect of the invention,computer 50 is programmed so that a physician can select one or moreanatomical structures using an input device 55, and the computer willthen highlight the periphery of that structure in any corresponding 2Dslice images displayed on display 60. See, for example, FIG. 16, where aboundary 110 is shown outlining the periphery of an object 115 displayedin a 2D slice image.

Other Modifications of the Basic System

Furthermore, while in the foregoing description the present inventionhas been described in the context of an anatomical visualization systembeing used by a physician, it is also to be appreciated that the systemcould be used in conjunction with inanimate objects being viewed by anon-physician, e.g., the system could be used to visualize substantiallyany object for which a 3D computer model and a collection of 2D sliceimage data can be assembled.

It is also anticipated that one might replace the polygonal surfacemodel discussed above with some other type of surface model. Thus, asused herein, the term “surface model” is intended to include polygonalsurface models, parametric surface models such as B-spline surfacemodels, quadrilateral meshes, etc.

Centerline Calculations

In yet another form of the present invention, the visualization andmeasurement system may incorporate means for determiningpatient-specific anatomical dimensions using appropriate scanned 2Dimage data.

For purposes of illustration but not limitation, this aspect of thepresent invention will be discussed in the context of measuring apatient's vascular structure in the region of the aortic/iliacbranching. By way of further example, such measurement might beconducted in the course of repairing an aortic aneurysm throughinstallation of a vascular prosthesis.

More particularly, using the aforementioned scanning device 5, a set of2D slice images is first generated, where each 2D slice imagecorresponds to a specific viewing plane or “slice” taken through thepatient's body. As noted above, on these 2D slice images, differenttypes of tissue are typically represented by different imageintensities. By way of example, FIG. 17 illustrates a 2D slice image 200taken through the abdomen of a patient, at a location above theaortic/iliac branching; FIG. 18 illustrates a 2D slice image 202 takenthrough the abdomen of the same patient, at a location below theaortic/iliac branching. In these images, vascular tissue might be shownat 205, bone at 207, other tissue at 210, etc. An appropriate set ofthese 2D slice images is assembled into a 3D database so as to provide avolumetric data set corresponding to the anatomical structure of thepatient. Referring back to the system illustrated in FIG. 6, the set of2D slice images making up this 3D database might be stored in secondsection 40 of data storage device or medium 30. In this respect it isalso to be appreciated that the 3D database being referred to now is notthe same as the 3D computer model contained in first section 35 of datastorage device or medium 30; rather, the 3D database being referred tonow is simply a volumetric data set made up of the series of 2D sliceimages contained in second section 40 of data storage device or medium30.

Next, using the appropriately programmed computer 50, thepatient-specific volumetric data set (formed out of the collection of 2Dslice images contained in the 3D database) is segmented so as tohighlight the anatomical structure of interest.

This is preferably effected as follows. On the computer's display 60,the user is presented with 2D slice images from the 3D database, whichimages are preferably stored in second section 40 of data storage deviceor medium 30. As noted above, each of these 2D images corresponds to aspecific viewing plane or “slice” taken through the patient's body; or,stated slightly differently, each of these 2D images essentiallyrepresents a plane cutting through the patient-specific volumetric dataset contained in the 3D database. As also discussed above, with each ofthese 2D slice images, the different types of tissue will generally berepresented by different image intensities. Using one or more of theinput devices 55, e.g., a mouse, the user (who might or might not be aphysician) selects a particular 2D slice image for viewing on display60, e.g., “slice image #155”. The user then uses one or more of theinput devices 55 to select one or more points located within theanatomical structure of interest. For convenience, such user-selectedpoints can be referred to as “seeds”. See, for example, FIG. 17, where aseed point 215 has been selected within the interior of vascular tissue205 so as to identify blood. The user also uses one or more of the inputdevices 55 to specify a range of image intensities that appear tocorrespond to the anatomical structure of interest in the volumetricdata set, e.g., blood within the interior of a blood vessel.

In accordance with the present invention, the appropriately programmedcomputer 50 then applies a segmentation algorithm of the sort well knownin the art to segment out related structure within the patient-specific3D database. Preferably computer 50 is programmed to apply a 3Dconnected component search through the volumetric data set contained insecond section 40 of data storage device or medium 30 so as to determinethe set of volumetric samples that are (i) within the range specifiedfor blood, and which (ii) can be connected along a connected path backto one of the seeds, where each of the locations along the path is alsowithin the range specified for blood. The result of this 3D connectedcomponent search is a set of 3D locations in the volumetric data setwhich correspond to blood flowing through the blood vessel. For thepurposes of the present illustration, this set of 3D locations can becharacterized as the “blood region”. The segmented anatomical structure(i.e., the blood in the blood region) can then be highlighted orotherwise identified on each of the 2D slice images. See, for example,FIGS. 17A and 18A, where the segmented blood region in vascular tissue205 has been cross-hatched to represent such highlighting.

Next, the branches in the segmented anatomical structure are identified.For example, and looking now at FIG. 19, in the present illustrationdealing with vascular structure in the region of the aortic/iliacbranching, the aorta and the two iliac branches would be separatelyidentified.

This is done in the following manner. For each of the vessel segmentsthat are part of the branching structure of interest, the user specifiesa branch line in the volumetric data set that uniquely indicates thatvessel segment. This is accomplished by using one or more of the inputdevices 55 to select, for each branch line, an appropriate “start”location on one of the 2D slice images contained within second section40 of data storage device or medium 30, and an appropriate “end”location on another one of the 2D slice images contained within secondsection 40 of data storage device or medium 30. It should be appreciatedthat these branch lines do not need to cover the entire length ofinterest of the vessel and, in practice, will tend to stop somewhatshort of the junction where various branches converge with one another.At the same time, however, for improved accuracy of modeling thebranching structure, the branch lines should extend close to thebifurcation point.

For each of the vessel branches, the start and end locations are used tosubdivide the blood region as follows: the region for that vessel branchis the set of locations within the blood region that are between thestart plane and the end plane, where the start plane for each vesselbranch is the 2D image plane passing through the start location for thecorresponding branch line, and the end plane for each vessel branch isthe 2D image plane passing through the end location for each vesselbranch.

Although the invention could be used for a more complex branchingstructure through obvious extensions, it is useful to consider a vesselbranch structure consisting of just three vessel segments comingtogether at a branch point, e.g., a vessel branch structure such as theaortic/iliac branching shown in FIG. 19. In this case, the user woulddesignate one vessel region as the root region (e.g., the aortic region220 defined by a branch line 225 having a start location 230 containedin a start plane 235, and an end location 240 contained in an end plane245) and the other vessel regions as branch region A (e.g., the iliacregion 250 defined by a branch line 255 having a start location 260contained in a start plane 265, and an end location 270 contained in anend plane 275), and branch region B (e.g., the iliac region 280 definedby a branch line 285 having a start location 290 contained in a startplane 295, and an end location 300 contained in an end plane 305),respectively.

For each of the vessel regions determined in the previous step, acentroid path is then calculated. This is accomplished in the followingmanner. First, at intervals along the vessel line corresponding to thevolumetric location of each of the original 2D slice images contained insecond section 40 of data storage device or medium 30, the centroid ofthe vessel region in that particular 2D slice image is calculated. Thisis done by averaging the image coordinates of all locations in that 2Dslice image that are within the vessel region so as to yield a centroidpoint. See, for example, FIG. 20, which schematically illustrates themanner of calculating the centroid 310 for a representative vesselregion 312 in a representative 2D slice image 315.

The centroid path for each vessel region is then established by thecollective set of centroid points located along that vessel segment inthree-dimensional space. The tortuous path corresponding to the rootregion is called the root centroid path and the tortuous pathscorresponding to branch regions A and B are called branch centroid pathA and branch centroid path B, respectively. See, for example, FIG. 21,which shows a plurality of centroids 320, a root centroid path generallyindicated at 325, a branch centroid path A generally indicated at 330,and a branch centroid path B generally indicated at 335, all shown inthe context of a vessel branch structure such as the aortic/iliacbranching example discussed above. It is to be appreciated that nocentroids will be defined in the “unknown” region 336 bounded by the endplane 245 and the start plane 265, and the “unknown” region 337 boundedby the end plane 245 and the start plane 295.

The system is programmed so that it will then apply a curve-fittingalgorithm to the tortuous centroid paths determined above so as tosupply estimated data for any portions of the anatomical structure whichmay lie between the aforementioned branch lines, and for “smoothing out”any noise that may occur in the system.

This is preferably done through a spline fitting algorithm effected inthe following manner. First, two new paths are created, by concatenatingthe points in the root centroid path 325 with the points in each of thetwo branch centroid paths 330 and 335, so as to create a path root-A anda path root-B. These two new paths are then used as the input to aspline fitting routine which selects the coefficients for a piecewisepolynomial space curve that best approximates the points along the pathin a least-squares sense. The number of pieces of the approximation andthe order of polynomial may be varied by the user. The resulting curvesmay be called spline-root-A and spline-root-B. See, for example, FIG.22, which illustrates the spline-root-B, generally indicated at 340.

Through numerical integration, the distance along the two splines (i.e.,spline-root-A and spline-root-B) can then be calculated using standard,well-known techniques, and the result can be presented to the user.These calculations can be used for a variety of purposes, e.g., to helpdetermine the appropriate size of a vascular prosthesis to be used inrepairing an aneurysm at the aortic/iliac junction.

In addition, using well established mathematical techniques, at anypoint along the spline paths, a tangent vector and a perpendicular planecan be readily determined either by direct calculation or by definitionin those cases where direct calculation would be undefined. Bycalculating the distance from the spline path to the points in thevolumetric data set corresponding to the vessel branch region that arewithin an epsilon distance of the perpendicular plane, the shape of thevessel at that point can be determined, and the radius of a circle thatbest fits the cross-sectional area of the vessel at that point can alsobe readily calculated. Again, this result can be used to help determinethat desired graft shape.

FIG. 23 is a flow chart illustrating how patient-specific anatomicaldimensions can be determined from scanned 2D data in accordance with thepresent invention.

In addition to the foregoing, it is possible to use the centerlinederived above to generate additional views for the observer, and/or tomake further anatomical calculations and measurements.

Oblique Slices Derived from the Centerline

Among other things, it is possible to use the centerline derived aboveto construct a series of oblique slices through the volumetric data set(which volumetric data set is formed out of the assembled scanned 2Dslice images contained in second section 40 of data storage device ormedium 30) such that the reconstructed oblique slices are disposedperpendicular to the centerline.

More particularly, oblique slices per se are generally well known in theart, to the extent that such oblique slices are arbitrary planarresamplings of the volumetric data set. However, the utility of thesearbitrary oblique slices is limited for many applications, since thereis no explicit, well-defined relationship between their position andanatomical structures of interest. By way of example, in the case ofblood vessels, oblique slices taken perpendicular to the length of theblood vessel are of particular importance to the physician. However,when generating oblique slices using traditional techniques (e.g., bypointing with an input device 55 while viewing the display 60), it isvery difficult for the physician to specify the oblique slice which istruly perpendicular to the blood vessel at a specified point. Thisproblem is avoided with the present invention, which utilizes thecenterline as derived above to generate the set of oblique slices lyingperpendicular to the blood vessel. This set of oblique slices derivedfrom the centerline is preferably stored in a fourth section 400 of datastorage device or medium 30 (FIGS. 5 and 6).

In general, one way to think about generating any oblique slice is toconsider a four-sided polygon that is placed in the space defined by thevolumetric data set. This polygon is then scan converted to resample theaxial images so as to generate the oblique slice desired. As usedherein, the term “scan converted” is intended to refer to the well-knowntechniques of subdividing a polygon into regularly spaced intervals on arectangular grid.

In the present invention a programmable computer is used to generate thespecific set of oblique slices that is defined by the centerline derivedabove. This is accomplished as follows. First, the centerline is dividedinto n increments. This can be done with points P₀, P₁, . . . , P_(n),as shown in FIG. 24. A line T_(i) is then derived for each of the pointsP_(i), where T_(i) is the tangent line at that point P_(i). Finally aseries of oblique slices are produced by constructing a series offour-sided polygons, each of which is centered at P_(i) and normal toT_(i). The locations of the corners of the polygon are selected suchthat the resulting image orientation is as close as possible to apre-selected image orientation (e.g., axial). These four-sided polygonsare then scan converted as described above so as to provide the set ofoblique slice images lying perpendicular to the centerline. As notedabove, this set of oblique slice images is stored in fourth section 400of data storage device or medium 30. At the same time, the cornerlocations of each four-sided polygon associated with each oblique sliceimage is also stored in fourth section 400 of data storage device ormedium 30, whereby the precise location of each oblique slice imagewithin the volumetric data set is established.

As a result of the foregoing, the oblique slice images stored in fourthsection 400 of data storage device or medium 30 is available to beaccessed by computer 50 in exactly the same manner as the 2D axial sliceimages stored in second section 40 of data storage device or medium 30.

Furthermore, once the aforementioned oblique slices have been derivedfrom the centerline, these oblique slices can then be used for a varietyof additional purposes.

Measuring Diameters Along the Centerline

As noted above, the oblique slice images derived from the centerline canbe accessed by computer 50 from fourth section 400 of data storagedevice or medium 30. The physician can then use input devices 55 toinstruct computer 50 to access the oblique slice at a particularlocation along the blood vessel and measure the diameter of the same. Inparticular, the physician can use input devices 55 to access theparticular oblique slice desired and then lay down twodiametrically-opposed marks so as to define the diameter of the bloodvessel; the computer is adapted in ways well known in the art to thencalculate the distance between the two marks. In this respect it shouldbe appreciated that since the aforementioned oblique slice images are,by definition, taken perpendicular to the blood vessel at each pointalong the blood vessel, the blood vessel diameters so measured will tendto be much more accurate than diameters calculated solely off axialslice images, and/or off coronal and/or sagittal and/or “standard”,non-centerline-derived oblique slice images.

Measuring Distances with a Cumulative Sum Table

It has also been found that it can be advantageous to store theincremental distances between the centerline points P₁, P₂, . . . ,P_(n) in a cumulative sum table in which the first entry, C₀, is 0; thesecond entry, C₁, is the distance between P₁ and P₀ (i.e., C₁=P₁−P₀);the third entry C₂=C₁+(P₂−P₁); etc. Thus, the centerline distancebetween any two points P_(i) and P_(j) is simply D_(ij)=C_(i)−C_(j).

In the present invention, the cumulative sum table can be of the sortshown in FIG. 25. This cumulative sum table is preferably stored in afifth section 405 of data storage device or medium 30 (FIGS. 5 and 6).Computer 50 is also programmed so that the user interface presents acenterline length calculation dialogue box 407 (FIG. 26) to thephysician on display 60, by which the physician can specify (using inputdevices 55) two oblique slice images which are the end points of thelength which is to be determined. Computer 50 is programmed so that itwill then determine the length between the two chosen oblique slices bycalculating the difference in their positions from the cumulative sumtable.

Computer 50 is also programmed so that a 3D graphical icon 408 (FIG. 27)is inserted into the 3D model contained in first section 35 of datastorage device or medium 30. This icon represents the portion of thevessel centerline which has been specified by the physician via the twooblique slice images which represent the length end points.

Calculating Volumes Using a Cumulative Sum Table

A cumulative sum table can also be used to calculate volumes withrespect to an anatomical structure, in much the same way that acumulative sum table can be used to calculate lengths along ananatomical structure. However, incremental slice volumes are moreappropriately calculated in the axial direction rather than in theoblique slice direction. This is because the axial slices all lieparallel to one another, whereas the oblique slices (since they aregenerated from the centerline) do not.

To this end, a computer is used to calculate the volume of each axialslice, V_(i), by (1) determining the number of pixels in the segmentedregion of that axial slice, (2) scaling by the appropriatepixel-to-length factor, and then (3) multiplying by the slice thickness.A cumulative sum table is then generated, where the first entry, C₀, isV₀; the second entry, C₁=C₀+V₁; the third entry C₂=C₁+V₂; etc. In thepresent invention, this cumulative sum table can be of the sort shown inFIG. 28. This cumulative sum table is stored in sixth section 410 ofdata storage device or medium 30. Computer 50 is also programmed so thatthe user interface presents a volume calculation dialogue box 412 (FIG.29) to the physician on display 60 that allows the physician toconveniently specify two axial slices as the end points of the volume tobe determined. Computer 50 then calculates the volume for the regionspecified, using the cumulative sum table. Computer 50 is alsoprogrammed so as to place a 3D graphical icon 415 (FIG. 30) in the 3Dmodel contained in the first section 35 of data storage device or medium30. This icon represents the volume specified by the physician using thevolume calculation dialogue box.

Virtual Grafts

In the preceding description, anatomical 3D computer models were createdfrom software objects representing anatomical objects (e.g., a firstsoftware object to represent a liver, a second software object torepresent an aorta, etc.); and additional software objects were createdto represent non-anatomical objects (e.g., markers 85, margins 105,boundaries 110 and graphical icon 408); and the various software objects(representing both anatomical and non-anatomical objects) were placedinto proper registration with one another using techniques well known inthe art so as to form a cohesive database for the application program'simage rendering software. Accordingly, the program's image renderingsoftware can render images showing both anatomical objects andnon-anatomical objects from various points of view, with the anatomicalobjects and the non-anatomical objects being in proper registration withone another.

In this respect it should be appreciated that it is also possible tocreate further software objects, in addition to those anatomical objects(e.g., liver, blood vessels, etc.) and non-anatomical objects (e.g.,markers 85, margins 105, boundaries 110 and graphical icon 408)disclosed above, and to place those additional objects into the system'sdatabase for selective viewing by the system's image rendering software.

Of particular significance is the ability to create software objectsrepresenting surgical (including implantable) devices, and to place suchsoftware objects in registration with software objects representing apatient's anatomy, in advance of an actual surgery, whereby to enhanceappropriate implant selection and facilitate surgical planning.

By way of example, and looking now at FIG. 31, there is shown a softwareobject 500 representing the aorta of a patient. Also shown is a seriesof markers 505 placed into the system (e.g., by a human operator using amouse) and a series of line segments 510 extending between selected onesof the markers 505. These markers 505 and line segments 510 may be usedto plan a surgical procedure, to determine anatomical lengths or angles,etc.

Also shown is a straight tube 515 which may also be used for planningand measurement purposes, etc., a curved tube 520 which may be used forplanning and measurement purposes, and a box 525 which may be used forplanning and measurement purposes, e.g., for volume calculations.

FIG. 32 is similar to FIG. 31, except that aorta 500 has been renderedtransparent.

In addition, other geometric elements such as curved lines, intersectinglines, etc. may also be provided for planning and measurement purposes.

Significantly, it is also possible to insert into the system softwareobjects representing virtual grafts, virtual implants, virtual devices,etc. By way of example, in FIG. 33 there is shown a virtual graft 530which represents an arterial stent which may be deployed in the aorta,e.g., to treat an aortic aneurysm.

Virtual Grafts (VG's), Manufacturer Specific Virtual Grafts (MSVG's),Twisteroo™, Native Iliac Rotation (NIR) and TwisterooNIR™ Click-DragDistance Calculation and Mark Name/Type Dichotomy

11.1 Virtual Grafts (VG's). Looking next at FIG. 34, in simpler versionsof the aforementioned Virtual Graft (VG) for aortic stent applications,users are able to place idealized tubes into the aorta model. The VGhelps users visualize what the surgery will look like and stems from themore basic Centerline Calculations discussed above.

In one simple preferred construction, a VG consists of three tubesarranged like a pair of pants. One of these tubes represents the “trunk”of a bifurcated stent graft and the other two tubes represent the legs.Users are able to define the length and diameter of the three tubes but,in this simpler version of the system, must perform calculations ontheir own to calculate the overlap that is used in placing the partsduring surgery. With this form of the invention, it is essential thatthe doctors be familiar with the dimensions of the product offeringsfrom all Abdominal Aortic Aneurysm (AAA) implant manufacturers, becausethe doctors must add the lengths of the pieces themselves, account foroverlap, etc.

11.2 Manufacturer Specific Virtual Grafts (MSVG's). In a moresophisticated form of the invention, Manufacturer Specific VirtualGrafts (MSVG) allow users to select and visualize actual stent graftdevices within patient-specific 3D anatomy. This MSVG feature simplifiesand enhances the vascular surgeon's experience in fitting an endoluminalimplant in three principal ways.

(i) Accurate Graft Information. First, the user does not have toremember the graft pieces available from a given manufacturer. With theMSVG graft designer, users simply choose from a list of all availablepieces for their chosen manufacturer. For example, rather than having toremember that W.L. Gore Excluders come in a 23 mm by 14 mm by 160 mmsize with a product code of “PCT231216”, the user will be able to choosethis part from a list of all W.L. Gore parts and the software systemwill both display the correct piece and keep track of the selected partnumber. This feature prevents users from recording the wrong values andspeeds their ability to evaluate how different parts will work in theanatomy. The software system internally keeps a catalog of manufacturerproduct codes, part geometries and compatibility criteria from componentto component.

(ii) Detailed Graft Visualization. A second, and perhaps most importantadvance with the MSVG, is the more detailed representation of thegrafts. Because endovascular AAA repair is a surgery that generallyrequires more than one surgical device to be implanted in the anatomy,the MSVG feature is also able to model multiple graft parts at one time,as well as the interaction of their overlap. AAA surgery usuallyrequires, at the minimum, a separate stent graft or “docking limb” to beinserted up the contralateral side of the patient and deployed insidethe previously-deployed bifurcated piece. See FIGS. 35 and 36, whichshow an MSVG before and after docking of a contralateral limb.

For most endovascular surgeries with docking limbs, it is important forthe doctor to understand how much the pieces overlap because thisdistance is important to reduce the risk of slippage and/or endoleak.Each manufacturer will typically specify the amount of overlap that isrequired to safely deploy a given component pair. The software systemis, in one preferred embodiment, able to model up to 9 different graftdevices in the same patient, specifically: 1 bifurcated piece, 1contralateral leg, 6 extenders and 1 aortic extender. To represent thisaspect of surgery, the MSVG feature colors the pieces differently basedon the amount they overlap each other and their respective sizes. SeeFIG. 37. The “yellow zone” in the figures represents “over-sizing” whichis similar to the physical overlap but is, in some ways, a more accurateway to understand the interaction. More particularly, it can be a moreuseful indicator because it represents the amount of surface-to-surfacecontact that the pieces will have when deployed and this over-sizing isoften what actually holds the pieces together.

The difference between overlap and “over-sizing” can be seen in FIG. 37.Here there is a contralateral leg with a smaller, tapered, extender.Again, the yellow zone represents overlap, but note that the yellow zonedoes not extend all the way to the bottom of the leg. This is becausethe extender piece that has been inserted tapers to a diameter smallerthan the enclosing piece. When this occurs, the extender piece will notactually press against the inside walls of the enclosing piece and thuswill not be over-sized.

There are three additional significant improvements to the graftrepresentations in a preferred MSVG feature. First, the grafts can havevariable diameters along their lengths. These increasing or decreasingtapers come directly from the manufacturer specifications and are quitedetailed. For example, a bifurcated piece such as the one in FIG. 35 canhave a diameter change along the length of its leg, allowing for a“bell-bottomed” or tapered leg. While not all manufacturers' pieces willinclude such a diameter change, those that do are now modeled moreprecisely.

The last two visualization features are the inclusion of arepresentation for graft hooks and the ability to make a grafttransparent. Graft hooks, which are typically metal prongs used tosecure a graft to the blood vessel, can be displayed using the MSVGsimulator as a red circle around the end of the graft. This allowsdoctors to judge the hook's location relative to the anatomy. Finally,transparent grafts can be used with a visible anatomy to judge the“over-sizing” of a graft relative to both the blood flow anatomy and thethrombus.

(iii) Increased Reliability. The third way that the MSVG enhances theuser's experience is through the increased reliability of the system.From beginning to end, the user is aided in choosing the right parts andis less prone to transcription errors from planning to surgery, orproblems that can arise due to incompatible parts.

Increased reliability starts with the new MSVG Designer (see FIG. 38).First of all, the Designer displays all of a user's relevantmeasurements from their session in the left hand pane. In the right handpane, there is a list of bifurcated pieces sorted horizontally bylength, vertically by iliac diameter and sectioned vertically by aorticdiameter. There is also a list of contralateral legs and a tree foriliac extenders. All of the buttons dynamically change their enabledstatus depending on the user's selections. This interaction implies thatchecking is performed to make sure that all selected sizes arecompatible. The MSVG Designer also checks to make sure that all of theindicated overlaps are within the manufacturer's guidelines for requiredoverlap. The Designer software adds up the length of both thecontralateral and ipsilateral sides, subtracting overlaps and displaysthis number in the two length boxes at the bottom left hand side of themeasurement panel. The MSVG Designer also includes a cascading list forselecting the amount of “Twisteroo™” for the graft. This feature isdiscussed in detail below.

After the user clicks “Build”, the program runs final checks to makesure that the selected grafts will display properly in the anatomy. Ifthese pass, it is then on to the visualization module, where the productcodes are turned into images and used as texture maps for the 3Dcreation of the graft. In this way, the vascular surgeon can tellimmediately by looking at the Model Window which manufacturer componentsare being displayed.

In the Product Listing page (see FIG. 39), the user can add any moreparts to include in their plan. Different endovascular devices requiredifferent sized sheaths for deployment, so users can also include thesein the Product Listing dialog. Because all surgeries generally requirethese sheaths, this page will of course warn users of any attempt tocontinue without ordering sufficient and correctly sized sheaths.

Finally, the desired graft component quantities are transferred via theInternet to a remote server where they are inserted into an Adobe PDFform (see FIG. 40) which is then kept with the model information on aremote server. This form is accessible over the Internet so that userscan print it out and send it in, or use it for later reference. Further,the information for the desired graft can be sent directly to the stentgraft manufacturer as part of an automated supply chain managementsystem.

This order form is the completion of the validated and reliable transferof information from the graft manufacturers' internal specifications, tothe MSVG Designer, to the visualization module and finally to componentorder fulfillment. This entire process has been designed to prevent theerrors caused by either working with incorrect data, not understandingspecifications properly, and/or mistyping or otherwise confusing catalogitems, from start to finish.

11.3 Twisteroo™. During endovascular AAA repair, a common surgicaltechnique is to rotate the proximal end of the bifurcated endoprosthesisbefore it is deployed and then to pass the contralateral leg, eitheranterior or posterior, to the bifurcated leg before docking it. Thistechnique is popular for many reasons. In some anatomies, it allows fora straighter shot out of the iliacs, making for an easier surgery. Somedoctors also feel that it can either improve the device seal or canreduce the pressure from the blood flow on the graft. It can also simplybe a useful method of deploying a graft to take up some of the “slack”in the limbs. By forcing a graft into a twisted configuration, it willpresumably take a longer path, effectively shortening its run down theiliacs. This can be especially pertinent when occlusion of the internaliliac artery is a concern.

Previously, there has been no way for a surgeon to model this techniquein a pre-operative effort to visualize the resultant graft paths or togauge the effective “shortening” that this technique will have on theoverall length of the graft. With the Twisteroo™ feature, users now havea tool to model various degrees of graft twist within a 3Dreconstruction of the anatomy.

The Twisteroo™ calculation. From a high level view, the basic idea ofthe twist calculation is to create two new “twist lines”, one for eachiliac, which begin at the end of the graft trunk and continue until theoriginal centerline splits. At this point, the graft will switch tracksand jump back onto the pre-existing right iliac leg (RIL) and left iliacleg (LIL) centerlines. The existing centerlines are preferably usedbecause they are a reviewed and validated system to predict the generalpath a graft will take though the anatomy. The twist lines start at theend of the graft trunk because the trunk will simply follow regularcenterlines. Once the twist calculation is finished, the grafts beginusing the regular RIL and LIL centerlines again, because they willcorrectly model the behavior of a graft leg through a tortuous anatomy.Thus, the Twisteroo™ is meant to model twisting primarily in theaneurismal sac. FIG. 41 is an example of two twist lines created for a180-degree twist and FIG. 42 is an example of the Virtual Graft once ithas followed the twist.

In this Twisteroo™ product, the iliac branches are assumed to lie in thecoronal plane.

The first calculation made in the creation of a twist is to calculatethe “spread” variable. This is how far the two legs will be pushed offthe centerline as they spiral down. This spread=½ (Left legdiameter/Right leg diameter) which comes from either the MSVG devicesizes or a user's generic device parameters. This calculation accountsfor potentially different leg diameters for each leg.

The second calculation made is to determine where the twist lines shouldend. This is calculated for each side, and is termed the “attachment”site. In FIG. 41 above, this is the point on the green line, where thegray line ends. This point is calculated by running down the centerlineuntil the RIL and LIL cubes are separated by a distance greater than the“spread”. This is where the graft stops following the twist lines andjumps back onto the regular centerline. It is related to the spreadbecause once the centerlines are that distance apart, the graft limbsare no longer capable of intersecting each other.

Spline Creation. Looking next at FIG. 43, splines are a way ofconnecting points or interpolating between points in a smooth andcontinuous manner. To do this, a spline takes into account a curve'senergy and tries to connect the points in a smooth way. Catmull-Romspline formulation is preferably used because it interpolates throughall of the given control points and is resistant to kinking.

Six control points are used per side to create the spline. With the“septum” defined as the end of the graft trunk, there is one controlpoint set proximal to the septum by 25 mm, one point at the septum, twomid-aneurysm control points each ⅓ of the way from the septum to thesides attachment, and finally one point at the attachment and one 25 mmdistal to the attachment. The two points located 25 mm away from theends of the graft are there to influence the path of the graft above.Their location along the centerline influences the endpoint tangents ofthe resulting splines so that the curve continues smoothly out of theiliac artery.

The next step is to add the “spread” into the equation in a way thatnaturally twists the graft down the length of the sac. To do this themost proximal 4 control points are translated away from the basiccenterline. Through basic trigonometry, the degree of twist is plottedon the unit circle and the x and y components of the resulting vectorobtained. It is known that at the bottom it is desirable to be directlyon the centerline, so the amount of rotation is reduced smoothly as thecenterline proceeds distally. Thus, for a 180 degree twist, the firsttwo control points will be translated directly away from their eventuallocation, while the middle control points will be translated at 120 andthen 60 degrees away. All translations are performed in the plane of thecenterline cube that they are based on. With these 6 control points, aCatmull-Rom spline is created and the results stored.

Contact. Looking next at FIG. 44, the resulting splines can still end uprunning through each other, because each side has so far been created inisolation. Therefore, the next step is to implement a simple contactmodel. A preferred contact model is basically a function that incrementsdown each of the twists, finding the nearest neighbor in the other twistline. Once it finds this neighbor, it then calculates the distancebetween them and then pushes the two points away from each other untilthey are at least the “spread” value apart. Any contact that is notremoved from the legs via this algorithm is modeled later during thevisualization process by calculating the distance from leg to leg, andthen adjusting the geometry of the graft limbs to “ovalize” them with aminor axis in the direction of the opposite leg.

Filter. Finally, the point locations are convolved through a largetriangle filter (30-way) which smoothes out any irregularities leftbehind by the twisting and contact process described above. Thissmoothing can result in reducing the distance between the two legs belowthe “spread” distance, which is actually a desirable effect because itallows the “ovalizing” process above to partially model the graft'sactual deformation.

Completion. Finally, the files TwistLineRIL.asc and TwistLineLIL.asc arewritten out in an .asc format. Because the orientation of the resultingcubes is important for texturing and visualization purposes, a functionis used to orient the cubes until they both face each other, but alsoline up smoothly with the corresponding first and last cubes on theoriginal centerlines. Because these are two distinct orientationconstraints, a function is used to blend the effect of each method basedon where the cube is on the centerline. Preferably a polynomial functionis used, such as y=x⁸, which produces a graph with a characteristicallywide base and highly sloped sides. Thus, the first and last cubes aremore heavily weighted at the beginning and end of the twist line, butalmost all orienting is done towards the neighboring cube through themiddle of the twist line.

The MSVG can now be drawn along the twist lines. The most importantbenefit of this feature is that it can actually model the shorteningthat a twisted graft's legs will undergo relative to their finallocation in the iliacs. Previously there was no good way to account forthis, and it was often simply assumed that it would shorten the graft byseveral millimeters.

11.4 Native Iliac Rotation (NIR) and TwisterooNIR™. In an improvedversion of the system, the system is capable of recognizing Native IliacRotation (NIR) and provides a TwisterooNIR™ product which takes NativeIliac Rotation (NIR) into account when conducting twist calculations.

Native Iliac Rotation (NIR). During the development of the originalTwisteroo™, it was noticed that, for some anatomies, the “neutral”amount of twist (or 0 degrees) was actually not the most natural fit forthe graft, since the bifurcation of the iliac arteries does not alwaysoccur in the coronal plane. Instead, it was found that in someanatomies, the bifurcation of the iliac arteries occurs at an angle fromthe coronal plane, i.e., the iliac arteries branch off in a twistedfashion, with one iliac more anterior than the other. For the purposesof the present invention, the term Native Iliac Rotation (NIR) can beused to describe the degree of twist of the iliac arteries away from thecoronal plane.

Looking now at FIG. 45, there is shown an axial CT scan slice (left sideof figure) just below the bifurcation point, and a virtual 3D model(right side of figure) showing the iliac branches extending out of thisslice plane. These images show how the two iliac arteries may branch offfrom one another. More particularly, FIG. 45 shows an example of ananatomy wherein one branch of the iliac artery is significantly moreposterior (i.e., closer to the backbone or bottom of the image) than theother branch.

Since the branching of the iliacs does not always happen strictly to theleft and right of the anatomy (i.e., with a 0 degree twist off thecoronal plane), the aforementioned Twisteroo™ technique for calculatingthe virtual graft twist does not always result in an accurate assessmentof the optimal twist for some patient-specific anatomies.

Accordingly, in one preferred embodiment of the present invention,sometimes hereinafter referred to as the TwisterooNIR™ product, there isprovided a new technique for measuring the NIR (i.e., the degree ofrotation off the coronal plane) of the iliac arteries, which is thenused to increase the accuracy of the aforementioned twist calculationand other tools and measurements.

Calculating Native Iliac Rotation (NIR). This technique begins bysimplifying the anatomy into two centerlines, as was previouslydiscussed above. These centerlines are formulated to travel down thecenter of each vessel as a series of cubes. From this formulation it iseasy to determine the XYZ location of any of the cubes in 3D space.

In order to measure the Native Iliac Rotation (NIR) of apatient-specific anatomy, three different centerlines are firstproduced: (i) a left iliac (LIL) centerline; (ii) a right iliac (RIL)centerline; and (iii) an aorta (AO) centerline (which is coincident withthe other two centerlines down through the aneurismal sac until the LILand RIL centerlines begin to diverge down the left and right sides ofthe bifurcation, at which point, the AO centerline continues to proceeddown the center of the anatomy, directly through the bifurcation and outa short way below the bifurcation.

Next, the XY positions (in the axial plane) of one point from the LILcenterline and one point from the RIL centerline are compared todetermine how much the points rotate away from the horizontal. In otherwords, the two points are compared to see how much each point is rotatedaway from the coronal plane. It will be appreciated that the comparedpoints from the LIL centerline and the RIL centerline preferably are atthe same position in the Z-axis (i.e., along the coronal plane). In onepreferred embodiment of the present invention, the left and right iliaccenterlines are compared at points approximately one half centimeterbelow the bifurcation.

In another embodiment of the present invention, the length of thecenterline is used as a guide to tell a user what part of the LIL andRIL centerlines to compare, since the AO centerline is always of alength defined to just make it past the bifurcation. More particularly,and looking now at FIG. 46, the total number of cubes in the AOcenterline is first determined, and then the same number of cubes isused to index into the left and right centerlines. Thus, if there are Ncubes in the AO centerline, the n^(th) cube of the LIL centerline(LIL[N]), and the n^(th) cube of the RIL centerline (RIL[N]), arecompared. For each of these cubes (i.e., LIL[N] and RIL[N]), the X and Ypositions (in 3D space) are determined. This method is furtherillustrated in FIG. 47, where a diagonal line has been drawn to extendthrough a centerline cube from both the left (LIL) and the right (RIL)centerline, and the horizontal line represents the coronal plane. Next,the differences (in X, Y terms) of the two points is calculated, andthen the inverse tangent of their quotient is calculated. The angle thusderived from these calculations is the Native Iliac Rotation (NIR) ofthe two iliacs away from the coronal plane.

TwisterooNIR™. Finding the Native Iliac Rotation (NIR) of apatient-specific anatomy allows the calculation of a more natural twistof the virtual graft for each specific patient. Previously, and as notedabove, the Twisteroo™ assumed that the natural state of the rotation wasat precisely 0 degrees (i.e., Twisteroo™ assumed that every patient hada “neutral” Native Iliac Rotation). This meant that if the physicianwanted to simulate a 180 degree twist, Twisteroo™ would simulate thegraft legs twisting from 180 degrees all the way back to 0 degrees. Inaccordance with the present invention, there is now provided theTwisterooNIR™ product, which uses the previously-calculated Native IliacRotation (NIR) when calculating for twist. TwisterooNIR™ simulates thevirtual graft legs twisting from the given degree of twist desired backto the patient-specific Natural Iliac Rotation. TwisterooNIR™ provides amore accurate simulation of the natural position at which the virtualgraft legs would be as they enter the iliac arteries. In particular,this is an advantageous method of simulating the twist of a graftbecause, in an anatomy with a high degree of native twist (e.g., a largeNatural Iliac Rotation), the graft's twist would end up turning tooquickly and in effect overshooting the target, or doing the reverse andnot twisting fast enough.

Previously, and as noted above, an algorithm would attempt to rotate thevirtual graft from an inputted degree of twist to 0 degrees, by buildinga spline along two control points spaced between the start and endpoints. The control points would be set so that ⅓ of the twist would beachieved by the first point, ⅔ of the twist would be achieved by thesecond point and the rest of the twist would be achieved between thesecond point and the end point, where the graft centerline rejoins theregular graft centerline. Thus, to achieve a 90 degree twist of thevirtual graft, the Twisteroo™ product would space control points at 66degrees and 33 degrees of twist. As mentioned above, this creates anundesired path in some instances. Specifically, in the case where apatient's iliac limbs are rotated 50 degrees relative to the coronalplane (i.e., the patient has a 50 degree Native Iliac Rotation) and a 90degree twist of the virtual graft is desired, the final point will be at50 degrees, and the control points will proceed thus: 90 degrees, 66degrees, 33 degrees, and 50 degrees, leaving an S-curve.

The TwisterooNIR™ performs its twist calculations by placing two controlpoints in between the beginning and end points just as the Twisteroo™algorithm did. However, the TwisterooNIR™ calculates the amount to twistdesired as:Total Twist Desired−Native Iliac Rotation=Amount To Twist The VirtualGraftFor the example noted above, the TwisterooNIR™ calculation comes out to90 degrees−50 degrees=40 degrees. The TwisterooNIR™ then divides theAmount To Twist The Virtual Graft (i.e., 40 degrees) by 3 and performsan interpolation to give control points at: 90 degrees, 76 degrees, 63degrees, and 50 degrees, leaving a much smoother curve than the S-curvedescribed above.

Looking now at FIG. 48, another example of the aforementioned problem isillustrated. This example illustrates a problem which may occur evenwhen the graft is set to 0 degrees of twist. The Twisteroo™ product ison the left and the TwisterooNIR™ product is on the right. The degree oftwist for both of these grafts is 0 degrees and the Native IliacRotation is 53 degrees. In the first case (i.e., the case on the leftutilizing the Twisteroo™ product), the control points are at: 0 degrees,0 degrees, 0 degrees, and 53 degrees. Since the algorithm cannot predictwhere the final point will be, it cannot approach this point gradually.This produces an unnatural “jerk” at the end of the graft. In theTwisterooNIR™ product, the control points are at: 0 degrees, 17 degrees,35 degrees, and 53 degrees. These control point calculations produce asmooth and more realistic curve for the graft path.

Because the grafts will be inserted in a manner that conforms to thetwist of the anatomy, the TwisterooNIR™ product reports the Native IliacRotation to the user so that they may consider simulating the graftdeployment in what has been calculated to be the natural state of theanatomy. Looking now at FIG. 49, this example shows how rotating thegraft to the Native Iliac Rotation can produce a subtly differentsimulation of the way that a surgery may actually proceed. FIG. 49illustrates how the graft legs are not required to do as much twistingwhen their rotation is adjusted to the Native Iliac Rotation (see theimage on the right) and FIG. 49 further illustrates how these twosimulations actually predict that the graft will terminate at a slightlydifferent place in the iliacs due to the difference in the graft path.

11.5 “Click-Drag” Distance Calculations. This new feature is a methodfor creating distance calculations. A distance calculation is defined asthe distance across the anatomy from one user-defined “Mark” to another.In simpler versions of the software system, a distance calculation canbe defined by selecting ‘New Distance Calculation’ from a menu. Thisopens a Dialog through which beginning and ending points can be selectedfor the calculation from a list of all available Marks. This process hasbecome much easier with the new method. To perform a “Click-Drag”distance calculation, the user simply has to click on the Slice Window,hold down the mouse button, and then drag the mouse to the desiredendpoint. The system software will then check to make sure that bothMarks of the calculation are within the slice volume and, if so, createtwo marks with a distance calculation between them. The system softwarewill also automatically change the size of the marks created for thestart and end points to be of a small size in order to reduce clutter onthe screen. One final feature of the “Click-Drag” distance calculationis that, if the user drags the mouse back within a minimum distance ofthe start point, the program will no longer perform a distancecalculation if the mouse is released and it will automatically returnthe size of the mark to normal.

11.6 Standard Mark And Calculation Types and the Name/Type Dichotomy.Another preferred new feature of the system is standardized Mark andCalculation types. In simpler versions of the system, Marks andCalculations could have names but these were user-defined and had to bemanually typed in for every instance. A simple user-defined name isinherently problematic when trying to compare one user's calculations tosomeone else's.

This simple naming scheme has been extended by adding a new standard“type” field to all Calculations and Marks. This new “name-type”dichotomy allows users to classify their measurements according to astandardized system while still adding their own names if they wouldlike. This can be particularly useful in the context of the softwaresystem where the same measurement can be made in different ways. The“Maximum AAA Diameter” type, for example, could be measured using eithera mark diameter or a distance calculation. For this case the user wouldgive all the measurements the same type, but different names.

As far as the interface is concerned, the first step after creating amark should be to select its type from menu. This menu is a drop-downlist with cascading submenus for aortic types, as well as right and leftiliac types. Once the user selects a type, the program willautomatically create an abbreviated version of name as the measurement'sname. The user is then free to modify this name if they would like to.The program will not overwrite any name that the user has alreadychosen. When a calculation is edited and the type changed, the programwill only change the name of the measurement if the old name was one ofthe abbreviated ones created by the program.

A list of all standard mark and calc types can be found in Appendix Aattached hereto.

Additional Feature

Iliac Access Tool

Another additional feature is the iliac access evaluator. This featureaddresses the need of the physician to evaluate the feasibility of anendovascular repair for a given patient. Obstacles to endovascularrepair include: calcium deposits within the blood vessels, excessivetortuosity of the blood vessels, and insufficient diameter of the iliacbranches (the iliacs). Physicians may need to choose between the devicesof different manufacturers based on the individual characteristics oftheir sheath products. Additionally, physicians will often have a choiceof which side to insert the main body of a bifurcated endoprosthesis,and which side to put the typically smaller diameter contralateral legdevice. For this reason, it can be important to be able to readilyevaluate the receptiveness of each iliac for a host of different devicesizes.

12.1 Sheath-Sizing Tool. The sheath-sizing tool is provided as avisualization aid for analysis of vessel diameters over the course ofthe iliac. The sheath-sizing tool displays virtual tubes for each of theiliacs of the vessel at a specified diameter. The virtual tubes begin atthe aortic bifurcation (calculated by using the end of the aorticcenterline) and terminate at the end of the pre-determined iliaccenterline. The diameter of each iliac's virtual tube is individuallycontrollable with a slider, and the transparency of the tubes can bechanged granularly from fully opaque to fully transparent. Where thevirtual tubes in the model appear to be bigger than the surroundingvessel, this represents areas where the given sheath will be larger thanthe vessel and possibly prevent iliac access.

More particularly, and looking now at FIG. 50, there is shown aschematic representation of the patient's anatomy, with the color red600 representing blood flow, the color blue 605 representing a virtualtube device of selected diameter, and the color yellow 610 representingplaque. In this view, the wall of the blood vessel is renderedtransparent, such that the blood vessel is essentially seen in thecontext of its internal blood flow. Furthermore, in this view, the userinterface 615 for the sheath-sizing tool is in the upper-left while thesemi-transparent virtual blue tubes 605 in the model window 620 to theright show the chosen sheath sizes relative to the 3D blood vesselmodel. The model tube 605 of the left iliac 625 is set to 18 French(fr)—a common unit for sizing sheaths and catheters—while the model tube605 of the right iliac 630 is at 20 fr.

The visualization for the virtual sheath-sizing tool builds uponstructures that have been described in the foregoing disclosure: the 3Dmodel of the blood vessel, the centerline structure that is constructedand the centerline calculations that are part of the present invention.Furthermore, the virtual tube devices 605 comprise virtual objects whichare inserted into the 3D computer model of the patient's anatomy.

12.2 Diameter Plot. The diameter plot is another tool that can be usedin the present invention to evaluate iliac access. Essentially, by usingthe pre-computed diameters of the iliac and displaying them along anaxis, a cross-sectional representation of the aorta can be generatedalong each iliac. By laying a line across this plot at a specifieddiameter, a visual indication can be obtained of how much of the vesselis larger than, or smaller than, the diameter represented by the lineacross the plot. Calcium and thrombus preferably show up separately fromthe lumen on this plot as well, aiding an evaluation of the plaque'slocation. The diameter plot tool can be intermingled with thesheath-sizing tool described above to afford two views of essentiallythe same information.

Looking next at FIG. 51, left and right iliac diameter plots are shownat 635 and 640, respectively. Length is along the x-axis while diameteris along the y-axis. In this figure, red 645 shows the diameter of thebloodflow lumen, yellow 650 is the thrombus and blue 655 is thecalcified plaque. Note that on the right iliac plot, around 175 mm,there is considerable calcification. The aforementioned plot line 660shows how much of the vessel is larger than, or smaller than, thediameter represented by the plot line.

The information used to construct the diameter plots has already beendiscussed above. More particularly, from the segmentation of the bloodvessel done in axial slices, and the centerline object of the bloodvessel that is calculated, reformatted (oblique) slices can be definedthat are always perpendicular to the centerline. By constructing obliqueslices of the underlying segmentation, the diameter along the vesselcenterline can be analyzed in a number of different ways.

Consider the bloodflow diameter. By counting the number of pixels ineach slice that labels blood and multiplying by the PixelSpacing(squared) conversion factor, the surface area of the blood can becalculated in each slice. Assuming the idealization that the vessel hasa circular shape perpendicular to the constructed centerline, the wellknown relationship for a circle of that area A can be used, i.e.,A=πr ²And so the diameter D isD=2r=2sqrt(A/π)

A second construction for the bloodflow diameter on an oblique slice isbased on first finding the centroid for the bloodflow segmentation.Successive chords can be drawn through the centroid with endpointsdefined where the bloodflow segmentation ends. The plotted diameter canthen be defined as the maximum chord that intersects the centroid foreach location along the centerline.

12.3 Coded Tortuosity. In an effort to better quantify the degree oftortuosity of a vessel, improved means have been devised for displayingthe tortuosity of the vessel (i) in the vessel, or (ii) on a diameterplot. There are many different methods for calculating tortuosity, andany of these can be the basis for this visualization. The codedtortuosity tool for displaying tortuosity on the vessel is very muchlike the visualization tools described above, except that the virtualvessel will be colored according to the tortuosity at each point alongits length. A simple stop light color-mapping scheme would give thephysician an immediate indication of where the highly tortuous areas ofiliac occur. The diameter plot can be colored according to this code aswell, thus alerting the physician to problematic conditions when thereis a combination of high tortuosity and calcium deposits or smalldiameter.

As mentioned above, centerline tortuosity can be defined in severalways. These include ratio of curved to straight-line lengths, average ofthe curvature, average of the curvature squared, average of themagnitude of the second derivative of the curve, etc.

Looking now at FIGS. 52 and 53, these figures show a tortuosity plotbased on the ratio of curved to straight-line lengths. Note that thisdefinition is meaningful only for a particular choice of window size.That is, for any location along the curved path, an interval must bechosen to define the endpoints for the ratio calculations. The coloredlines 665, 670, 675, 680 and 685 in the plots shown in FIGS. 52 and 53represent variable interval sizes from 20 mm to 100 mm.

12.4 Access Score. It is also possible to provide a total Access Scorewhich is a function of the risk associated with all of the variousmeasurable obstacles discussed above. The Access Score algorithm cantake into account such things as presence and thickness of calcium,tortuosity, vessel diameter along the entire length of the iliacs, etc.,and output a single score for a patient's candidacy for catheter-basedsurgery. This Access Score can be used as a quick assessment of apatient or for categorizing patients for further analysis of theirprocedure.

By way of example but not limitation, these relationships can beformalized as follows. The patient specific “access availability” (AA)is defined to be a function of the calcification, tortuosity anddiameter.AA=ƒ(calcification,tortuosity,diameter)The device-specific “access requirement” (AR) is a function of thedevice diameter and stiffness.AR=g(stiffness,device diameter)Then access in a given iliac is possible if AA>AR for the entire lengthof the vessel.

12.5 Calcium and Plaque Alerts. Calcium and plaque alerts can be setupto flash or otherwise distinguish the plaques deemed to be inproblematic positions by the algorithm described above. Using arrows inthe model window or diameter plot, or flashing the virtual structures onand off, dangerous plaques can be highlighted as an alert to potentiallyproblematic areas for femoral access.

Additional Feature

Automatic Cranio-Caudal Angle Calculation

The Automatic Cranio-Caudal Angle Calculation tool automates thecreation of an angle calculation based on a particular vesselcenterline. This saves the physician the time and effort involved intrying to describe an angle in 3-dimensional space. The tool begins bysimply taking the number of an aortic slice (see, for example, FIGS. 14and 31) at the press of a button. The tool then gets the orientation ofthis slice and calculates the angle of this slice in the sagittal planerelative to the axial plane. The Automatic Cranio-Caudal AngleCalculation tool places three marks, one in the center of the slice, onedirectly anterior to this mark, and one at the anterior crossing of thisoblique plane with the sagittal plane through the first mark. The angleis then calculated between these three marks, putting the mark in thecenter of the oblique slice at the apex of the angle. This anglerepresents the angle of the oblique slice in the cranio-caudal plane andis used for a physician pre-operative assessment of the proper C-Armangle.

Looking now at FIG. 54-56, FIG. 54 illustrates the geometry of the bloodvessel. The blue plane 700 is sagittal to the bloodflow through thecenterline at the proximal neck of the aorta. The purple plane 705 isperpendicular to the centerline at the same location. FIG. 55 shows ananatomical detail 710, with the bloodflow transparent. The lightinterior cubes 715 represent points along the centerline of the anatomy.

In this case, the C-arm gantry correction is defined to be the interiorangle from the intersection of the sagittal slice (blue) 700 to theaxial slice, and the intersection of the sagittal slice 700 to theoblique slice (purple) 705.

FIG. 56 shows the resulting angle calculation as the lines in green,i.e., a first point 720 in the center of the slice, a second point 725directly anterior to this mark, and a third point 730 at the anteriorcrossing of this oblique plane with the sagital plane through the firstmark. The intersection of the line 735 (defined by the points 720 and725) with the line 740 (defined by the points 720 and 730) defines theangle 745 of C-arm gantry correction. For this patient, the C-arm gantrycorrection is 11.5 degrees.

More particularly, suppose the location on the centerline is P_(cl). Thevector defined by the sagittal/axial intersection V_(sa) has a singledirection component along the y-axis of the coordinate system and can bewrittenV _(sa) =P _(cl)+{0radius0}The vector normal to the oblique (purple) plane 705 is the tangent tothe centerline curve, and may be called V_(cl) _(—) _(tan). Then theC-arm correction vector V_(carm) is simply the cross product,V _(carm) =V _(sa)crossV _(cl) _(—) _(tan)

13.1 C-Arm View. The C-Arm view tool takes the automatic anglecalculation described above one step further and allows the user tovisualize what the anatomy will look like after a cranio-caudal, andleft/right rotation, of the C-Arm. The C-Arm view tool works by takingthe same angle calculated above, but rather than creating an angle, itcenters the model window on the selected centerline cube and rotates theview until it is looking at the anatomy at this angle. The user may thenrotate the model, which now pivots around this new center axis. At alltimes the angle of the view in latitude and longitude is displayed inthe model window. When the physician is satisfied that they have foundthe ideal combination of left/right and up/down angle, they can click a“save” button, and the system will save this view along with the otherviews.

Tools and Definitions for Measuring

Large Vessels Such as the Thoracic Aorta

Two key features of the foregoing system are (i) the ability to makelength measurements along a three-dimensional centerline that isrepresentative of a blood vessel, and (ii) the ability to make volumemeasurements of that vessel. Centerline measurements are often used tocharacterize patient geometry for stent placement, such as the length ofthe non-aneurysmal proximal neck of an abdominal aortic aneurysm (AAA)or the expected length of a candidate graft. Longitudinal volumemeasurements have proven to be a good marker for device effectiveness.

These tools have proven very useful in characterizing AAA disease.However, larger, more tortuous vessels, such as the thoracic aorta,present unique challenges. The present invention comprises two newfeatures, tools and definitions for measuring large, tortuous vesselssuch as the thoracic aorta:

(i) Longitudinal Analysis Of A Generalized-Cylinder Constructed From ACurvilinear Centerline; and

(ii) The VolumeOblique Calculation.

14.1 Longitudinal Analysis Of A Generalized-Cylinder Constructed From ACurvilinear Centerline. The visualization software of the presentinvention may be used to aid physicians in the implantation of grafts orstents into various parts of the vascular anatomy. In any situation, butparticularly in the thoracic aorta where the curvature of the vessel canbe dramatic and the devices become much wider, there can be significantdifferences in the length along the inside and outside curves of anydevice that travels along the vessel. The problem can be wellrepresented by a simple diagram. See FIG. 57.

In FIG. 57, we examine a hypothetical tube device of width 28 mm as itgoes around a 90 degree corner. This approximates a graft with aninterior radius of 50 mm, a central radius of 63 mm and an outer radiusof 78 mm. A simple calculation (taking ¼ of the circumference of threedifferent circles with these diameters) shows us that the inner curve ofthis tube will be approximately 78 mm, the center curve will travel 100mm and the outer curve length is 120 mm.

The challenge arises when we seek to predict the excursion of a graft ofknown length (such as 100 mm) when implanted into a patient with highlycurved vessel geometry. Currently the vessel centerline is used for allgraft length calculations. This means that the curves above are a goodrepresentation for the current system if we were visualizing a 100 mmgraft with a diameter of 28 mm extending along a 90 degree corner. Usingthe centerline as the predictive path, however, assumes that the graftwill be equally capable of expanding to 120 mm on one side andcompressing to 78 mm on the other if it is to deploy as predicted. Whilemost grafts are able to both expand and compress in some manner, it isdesirable to know the minimum and maximum length that our predictedtubes will travel if we are to make better graft length predictions.

Furthermore, it is common in some TAA devices, such as the GORE TAGThoracic Endoprosthesis, in the Anatomical Requirements section of the“Instructions for Use”, to specify a minimum distance (such as 2 cm)from the left subclavian/left common carotid artery to the proximal endof the aneurysm. This minimum distance specification corresponds to the“outer curve” as described above.

14.1.1 Our Solution. Our solution is to measure the length along theperimeter of the device at a set numbers of “longitudes”. Because mostgrafts are more able to compress than expand, we may expect a morephysiologically relevant result if we limit our predicted extension tothat which has a maximum longitudinal length equal to the graft'snatural length.

FIG. 58 shows an example of a Virtual Graft visualization occluding ananeurysm while making a 90 degree turn. The thoracic aorta is frequentlythis tortuous. Also depicted in FIG. 58 are some of the 16longitudinally-distributed contours that are defined by this particular“generalized cylinder” representation.

These paths (i.e., the 16 longitudinally-extending lines) represent thecontour lines along which the length is calculated. The lines describedabove and depicted in FIG. 58 range from 170 mm to 228 mm in length. Thevessel centerline running down the middle of the device travels 199 mmfrom the beginning to the end of the virtual device.

14.1.2 Method For Longitudinal Analysis Along A Centerline. Listing 1outlines the basic algorithm for calculating the length along anarbitrary number of longitudes. The concept is to march down thecenterline, incrementally adding to a bank of longitudinal lengthcounters as we go. The amount to be added is calculated by looking atthe orientation of the centerline at the point in question. From thecenterline's orientation vector, we create a perpendicular vector. Fromthis new vector (i.e., the perpendicular vector), we rotate around thecenterline's axis by a number of degrees relative to the number oflongitudinal lengths to be calculated. Pushing this vector out to theradius of the tube gives us the location of a point on the outside ofthe tube. We then calculate the distance from this point to the lastpoint for this longitude and add this to the total length so far.

Note that the algorithm as described above lends itself easily to anumber of extensions.

First, the initial vessel centerline is not limited in any way; it candefine an arbitrary three-space path.

Second, the radius does not need to be constant; a convenientformulation is to make the radius a function of the arc-length along thevessel centerline. In this way, it is simple to characterize“graft-shaped” tubes.

In addition to the foregoing, a second analysis method has been added tohandle the case in which there is a significant amount of twist in theinput centerline. If the centerline twists, it is possible to find aminimum path along a single longitude that does not correspond to a“global” minimum. Additionally, the maximum longitude found in this casewill tend to spiral around the vessel and thus not correspond to the TAAanatomy of interest.

In order to handle this case of the centerline that includes a twistingcomponent, a “state-space” search algorithm, such as A* is employed tofirst find the shortest path on the TAA vessel, between a pair ofextents on the defined centerline. The “outer curve” can then beconstructed by rotating the “minimum points” by 180 degrees around thegiven centerline.

The A* cost function is easily defined through the construction of ourgeneralized cylinder as the straight-line approximation moving fromlatitude line to latitude line. Each state change can be optimized toconsider both the vertices and the interpolated path for each latitude.The goal state is defined as any point on the final latitude line.Finally, we can use the steps from the longitudinal analysis above todefine the heuristic component of the cost function needed by the A*search.

14.1.3 Summary. In summary, this new tool allows us to better predictthe extension of a tube along a curvilinear centerline. Previous methodsconsidered the length on only one path for a given centerline, namelythe centerline itself. This new method allows us to predict the lengthalong a number of paths, given a diameter (or diameter function) andcurvilinear centerline. The longest one of these paths is likely to be amore accurate predictor of the ending point for stents in situ.

14.2 The VolumeOblique Measurement.

14.2.1 Introduction. The change in total vessel volume is a criticalmeasure for assessing the effectiveness of surgical repair of aneurysmsin both the abdominal aorta aneurysm (AAA) and thoracic aorta aneurysm(TAA). The previous volume measurement calculates volumes throughcounting voxels within Regions of Interest (ROI, or segmentation)defined in the axial slices acquired from computed topographicangiography (CTA) imaging. However, this method is not as easilyutilized in the TAA case, since the ascending and descending portions ofthe flow lumen are both captured within the same axial image. It isimportant to measure volume changes in the ascending or descendingportion of the thoracic aorta independently for assessing changes withinthe TAA. Thus, there is hereinafter provided a novel volume measurementstrategy with the aid of oblique planes perpendicular to the vesselcenterline which provides a precise and convenient tool to calculatevessel volume along a medial curve.

14.2.3 Methodology. The two basic inputs to the VolumeObliquemeasurement are:

(i) ROIs derived from the medical image that define the vessel anatomyto be measured; and

(ii) centerlines that define the three-dimensional path taken by thevessel and from which oblique planes perpendicular to the vessel can bederived.

The VolumeOblique measurement comprises the technique of integrating thesurface visualization with medical image processing, for which foursteps are performed:

(A) selection of beginning and ending planes for the oblique volume;

(B) volume removal through the 3D seed flood algorithm through selectedROIs;

(C) partitioning of the oblique volume through analysis of the vesselcenterline to define the “integrable” space; and

(D) VolumeOblique measurement reporting.

The workflow for creating the VolumeOblique measurement is shown inFIGS. 59, 60 and 61. FIG. 59 shows the original surface model definingthe TAA within the source CT scan. FIG. 60 shows the selection of theoblique volume endpoints with two oblique planes. FIG. 61 shows thesurface model of the target volume to be reported after theVolumeOblique method has been run.

14.2.3A. Selection of Beginning and Ending Planes for the ObliqueVolume. The present system provides the tools to construct the 3D shadedgeometric surface model of blood flow, calcified plaque, and thrombusfrom the regions of interest defined by pre-segmented data. The medialcurve paths (centerlines) are automatically extracted for aorta, aortaleft iliac, and aorta right iliac arteries. The oblique planes alongeach medial curve path are reconstructed with a multi-planarreformatting (MPR) algorithm.

For TAA data, the ascending and descending portions of aorta areacquired within the same axial image. The primary objective of thevolume oblique measurement is to find a way to divide the ascending anddescending portions of TAA into separate volumes. With two obliqueplanes (start and end planes) specified by the user interactively alongthe medial curve path, an enclosed region between two planes is definedas the target region for the volume measurement.

The parametric formulation of a 3D plane is represented by:N _(x) ·x+N _(y) ·y+N _(z) ·z=D  (1)in which the normal vector to the plane (N_(x), N_(y), N_(z)) definesthe space inside or outside of the plane.

The two oblique planes defining the end points for the calculation areformulated as:Start plane: A ₁ ·x+B ₁ ·y+C ₁ ·z=D ₁  (2)End plane: A ₂ ·x+B ₂ ·y+C ₂ ·z=D ₂  (3)in which (A₁,B₁,C₁) and (A₂,B₂,C₂) are the normal vectors of the startand end planes.

A closed oblique volume region will be defined by choosing two obliqueMPR planes: (1) outside the start plane toward the normal direction, and(2) inside the end plane toward the opposite direction of normal. Theoblique volume is represented by:

$\begin{matrix}\{ \begin{matrix}{{{A_{1} \cdot x} + {B_{1} \cdot y} + {C_{1} \cdot z}} > D_{1}} \\{{{A_{2} \cdot x} + {B_{2} \cdot y} + {C_{2} \cdot z}} < D_{2}}\end{matrix}  & (4)\end{matrix}$

14.2.3B Volume Removal Through 3D Recursive Seed Flood Through DefinedROIs. We apply volume removal instead of volume accumulation, since thelatter method has the potential problem of accumulating an enclosedoblique region more than once. In our strategy, the desired 3D volume isfirst removed between two oblique planes, then a “masking” operation isperformed to obtain the desired segmented volume that comprises ourtarget region.

The 3D seed flood algorithm is applied recursively for volume removal ona “6-connected” neighborhood. The points on the medial curve betweenstart and end planes are first appended onto a seeds list. If theinterior color is equal to the desired segmented region (blood flow,calcified plaque, and/or thrombus), the color of that voxel will bechanged to the mask color for volume removal. This algorithm for 3D seedflood removal is described as follows:

(1) Input x, y, z coordinates of seed, color of segmented areas(segColor), and color of mask (maskColor);

(2) If color (x,y,z)==segcolor, then color(x,y,z)=maskColor; and

(3) x=x+1, go to step 1;

-   -   x=x−1, go to step 1;    -   y=y+1, go to step 1;    -   y=y−1, go to step 1;    -   z=z+1, go to step 1;    -   z=z−1, go to step 1;

14.2.3C Partitioning Of The Oblique Volume. In some extreme cases, dueto the tortuous nature of the vessel, the start and end planes may notclearly define an isolated volume region. We will show such a difficultcase for volume oblique removal algorithm. FIG. 62 shows the originalsurface models of TAA data before the oblique volume removal. FIG. 63shows the surface models for the simple case where the start and endplane numbers are 65 mm and 360 mm from the TAA origin to the heart,respectively. FIG. 64 shows the difficult case when we select the startand end plane numbers as 115 and 360, respectively. FIG. 65 shows volumeoblique removal with incorrect result by using a single flood operation.

We have developed a novel strategy to partition the whole of the desiredvolume into sub-volumes, which are enclosed by two intermediate obliqueplanes between the selected start and end planes. Each time, we applythe seed flood removal within this new sub-volume and then repeat theprocess until the whole volume has been completely “masked”.

Consider the normal vector defined by each of the oblique planes alongthe centerline. Note that this vector corresponds exactly to the 3Dtangent along the curve and can be easily written as a tensor functionof arc length. The interior angle between any two vectors can be easilyfound by taking the dot product of those vectors.

The interior angle transition from ascending to descending portion ofTAA surface is dramatic. Because of the way in which the normal vectors“flip” from up to down, this angle can approach 180 degrees.

Our method for partitioning a three-space based on obliquely definedcutting planes is based on the angle changes along the medial curvepath. We search from the start plane and consider tangent vectors atincreasing arc lengths. If the angle change is equal to or greater than45 degrees, we select this plane as an intermediate end plane. Theregion between this intermediate end plane and start plane will betreated as a sub-volume. Then, we set the intermediate plane as thestart plane and continue this process until the whole volume is fullypartitioned into sub-volumes. Then the points of the medial curve withinthe sub-volume are added into the seed list (we preferably use 1 mmincrements).

This procedure for subdivision of the oblique volume by consideringangle changes for the curve's tangent vectors is illustrated as follows:

(1) search from the centerline point of start plane P_(start);

(2) calculate the angle change between the normal of the following planealong the medial curve path and that of start plane P_(start);

(3) if the angle change of the normal is greater than 45 degree, thenset this plane as intermediate end plane P_(end); the region betweenP_(start) and P_(end) is defined as a sub-volume;

(4) continue this process until the whole volume is divided intosub-volumes;

(5) the points along the medial curve within the sub-volume are appendedonto the seed list; and

(6) apply seed flood removal algorithm within each sub-volumecontinuously to remove whole enclosed volume.

FIG. 66 shows the anterior view of the surface model after VolumeObliqueremoval. FIG. 67 shows a detail of the cut plane around the arch regiontransition from ascending to descending after VolumeOblique removal.

14.2.3D VolumeOblique Measurement Reporting. An image volume will begenerated including the segmented areas after the volume obliqueremoval. The target volume is calculated by multiplying the number ofvoxels for the segmented area (blood flow, thrombus, and calcifiedplaque) with the physical volume of a voxel, which is expressed as:Volume=N·V _(pixel) =N·V _(x) ·V _(y) ·V _(z)  (5)in which N is the total number of voxels for the segmented area; andV_(x), V_(y) and V_(z) are the voxel spacing in x, y, z directions,respectively. For a typical CT scan, these values are 0.7 mm, 0.7 mm and2 mm.

FIG. 68 shows our graphical user interface (GUI) for performing theVolumeOblique measurement. The user can set the type of medial curvepath (aorta, aorta left iliac or aorta right iliac), select from amongpredefined regions of interest (bloodflow, thrombus, calcium, or all) aswell as the first and second oblique MPR planes. The volume of thedesired segmented area between two oblique planes is then calculated anddisplayed on the fly (e.g., typically about a second). The unit ofvolume is cubic centimeters.

14.2.4 Validation. To verify the accuracy of our volume obliquemeasurement algorithm, a file with the segmentation areas isautomatically generated which represents the object to be measured. The3D surface model of the object can then be built and visualized tovalidate the algorithm.

Another validation has been performed to ensure that the new volumecalculation algorithm provides an accurate measure of vessel volume forthe area defined. In order to confirm the volume calculation, we firstcreated a volume oblique measurement using this volume oblique strategyat the left carotid origin to divide the TAA into ascending anddescending portions.

An estimate of this TAA volume was then made by finding the volume ofthe whole TAA, then subtracting half the volume from just the archportion. This represents the only way with the current tools to estimatethe volume of the aorta in the region required and does notdifferentiate between aneurysm in the ascending versus descendingportions appropriately.

14.2.5 Conclusion. A novel strategy to measure volume oblique has beenprovided herein. By “integrating” the volume defined by pre-determinedregions of interest and user selected oblique cutting planes, itdemonstrates the ability to accurately measure TAA volumes. Experimentshave been conducted to validate this volume measurement algorithm, whichwe believe provides an accurate and convenient measure forcharacterizing the effectiveness of TAA repair.

1. A method for deploying a device in a tortuous vessel, comprising:storing a virtual representation of the tortuous vessel in a storagemedium; accessing, by a processor, the virtual representation of thetortuous vessel; placing, by the processor, a virtualgeneralized-cylinder within the virtual representation of the tortuousvessel; measuring, by the processor, length along the perimeter of thevirtual generalized-cylinder at a set numbers of longitudes;determining, by the processor, the maximum measured length; selecting,by a physician, a device based upon the maximum measured length; anddeploying, by the physician, the device in the tortuous vessel.
 2. Amethod according to claim 1 wherein the virtual generalized-cylinder isplaced within the virtual representation of the tortuous vessel by theprocessor (i) calculating the centerline of the virtual representationof the tortuous vessel, and (ii) generating the virtualgeneralized-cylinder by defining an extent along the centerline of thevirtual representation of the tortuous vessel and constructing thevirtual generalized-cylinder about the centerline.
 3. A method accordingto claim 2 wherein measuring length along the perimeter of the virtualdevice at a set numbers of longitudes comprises the processor marchingdown the centerline of the virtual generalized-cylinder, incrementallyadding to an array of longitudinal length counters as progressing alongthe centerline.
 4. A method according to claim 3 wherein the amount tobe added to the array of longitudinal length counters is calculated bythe processor performing the steps of: (i) looking at the orientation ofthe centerline at the point in question; (ii) determining aperpendicular vector; (iii) rotating around the centerline's axis by anumber of degrees relative to the number of longitudinal lengths to becalculated; (iv) pushing this vector out to the radius of the virtualgeneralized-cylinder so as to determine the location of a point on theoutside of the virtual generalized-cylinder; and (v) calculating thedistance from this point to the last point for this longitude and addingthis to the total length previously determined in the longitudinallength counter.
 5. A method according to claim 1 wherein the device isselected by the physician based upon the maximum measured length.
 6. Amethod for measuring a length along a tortuous vessel, comprising:storing a virtual representation of the tortuous vessel in a storagemedium; accessing, by a processor, the virtual representation of thetortuous vessel; placing, by the processor, a virtualgeneralized-cylinder within a virtual representation of the tortuousvessel; measuring, by the processor, length along the perimeter of thevirtual generalized-cylinder at a set numbers of longitudes; anddetermining, by the processor, at least one of the maximum measuredlength and the minimum measured length.
 7. A method according to claim 6wherein the effect of twisting of the virtual generalized-cylinder isremoved by the processor using a state-space search process.
 8. A methodaccording to claim 7 wherein the state-space search process is derivedby the processor using a cost function associated with measuring lengthalong the longitudes.
 9. Apparatus for use in measuring a length along atortuous vessel, comprising: a storage medium storing a virtualrepresentation of the tortuous vessel; and a processor accessing thevirtual representation of the tortuous vessel in the storage medium andexecuting software components for: (1) placing a virtualgeneralized-cylinder within a virtual representation of the tortuousvessel; (2) measuring length along the perimeter of the virtual deviceat a set numbers of longitudes; and (3) determining at least one of themaximum measured length and the minimum measured length.